Image read-out method and system, solid image sensor, and image detecting sheet

ABSTRACT

An image signal is read out by use of a stimulable phosphor sheet having a layer of stimulable phosphor which emits stimulated emission in proportion to the stored energy of radiation upon exposure to stimulating light and a solid image sensor having a photoconductive material layer which exhibits electric conductivity upon exposure to the stimulated emission from the stimulable phosphor sheet. Stimulating light is caused to scan a stimulable phosphor sheet which has been exposed to radiation and has stored an image, the photoconductive material layer is caused to be exposed to stimulated emission emitted from the stimulable phosphor sheet upon exposure to the stimulating light. Then electric charges generated in the photoconductive material layer upon exposure to the stimulated emission is detected by applying an electric field to the photoconductive material layer. The stimulable phosphor sheet has a layer of stimulable phosphor which is stimulated by stimulating light in a wavelength range of not shorter than 600 nm and emits stimulated emission in a wavelength range of not longer than 500 nm. The solid image sensor has a photoconductive material layer whose major component is a-Se, and the electric field is such as to generate an avalanche amplification effect in the photoconductive material layer.

This is a divisional of application Ser. No. 09/534,204 filed Mar. 24,2000 the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of and a system for reading out animage, a solid image sensor, and an image detecting sheet.

2. Description of the Related Art

When certain kinds of phosphors are exposed to a radiation such asX-rays, α-rays, β-rays, γ-rays, cathode rays or ultraviolet rays, theystore a part of the radiation. Then when the phosphor which has beenexposed to the radiation is exposed to stimulating rays such as visiblelight, light is emitted from the phosphor in proportion to the storedenergy of the radiation. A phosphor exhibiting such properties isgenerally referred to as “a stimulable phosphor”. In this specification,the light emitted from the stimulable phosphor upon stimulation thereofwill be referred to as “stimulated emission”. There has been known aradiation image read-out method or a radiation image read-out system inwhich a sheet provided with a layer of the stimulable phosphor (will bereferred to as “a stimulable phosphor sheet”, hereinbelow) is firstexposed to a radiation passing through an object such as the human bodyto have a radiation image of the object stored on the stimulablephosphor sheet, a stimulating light beam such as a laser beam is causedto scan the stimulable phosphor sheet so that the stimulable phosphorsheet emits stimulated emission as signal light bearing thereoninformation on the radiation image, and the stimulated emission isphotoelectrically detected, thereby obtaining an image signal bearingthereon a radiation image of the object. Further there have been knownvarious image read-out systems which are different in the manner ofscanning the stimulable phosphor sheet with the stimulating light beam,the form of the means for photoelectrically detecting the stimulatedemission, or the like.

For example, there has been known an image read-out method and an imageread-out system which include a stimulating light source which emitsspot light like a laser beam as the stimulating light, a photomultiplieras a zero-dimensional photoelectric convertor which converts stimulatedemission emitted from the stimulable phosphor sheet upon exposure to thespot light to an electric signal and a stimulating light scanningoptical system which causes the spot light to scan the stimulablephosphor sheet in a main scanning direction while moving the spot lightand the photomultiplier in a sub-scanning direction relatively to thestimulable phosphor sheet, and in which stimulated emission emitted fromparts of the stimulable phosphor sheet upon exposure to the spot lightis read in sequence by the photomultiplier. See, for instance, JapaneseUnexamined Patent Publication Nos. 55(1980)-12492 and 56(1981)-11395.

The photomultiplier comprises a photocathode face and an electronmultiplier portion, and is excellent in that since a weak signalgenerated by weak stimulated emission is amplified by an external photoelectric effect and accordingly, the electric signal obtained by thephotomultiplier is less affected by electric noise. It is preferred thatthe photocathode face of the photomultiplier is high in sensitivity tothe stimulated emission in a wavelength range of about 300 to 500 nm (ina blue region) and low in sensitivity to the stimulating light in awavelength range of about 600 to 700 nm (in a red region).

Further the photomultiplier may be have a circular or polygonalphotocathode face or an elongated photocathode face extending in alength substantially equal to the width of the stimulable phosphorsheet, and is used as a zero-dimensional sensor in either case. In theformer case, the photomultiplier is employed together with a light guidewhich is provided with an elongated light inlet end face extending in alength substantially equal to the width of the stimulable phosphor sheetand a light exit end face connected to the circular or polygonalphotocathode face of the photomultiplier.

However, when such a photomultiplier is used, the following problemsarise.

(1) The photomultiplier comprises a vacuum glass tube, and accordinglyis fragile.

(2) The photomultiplier comprises a complicated multistage diode forelectron multiplication, and accordingly is difficult to reduce thethickness. Further, a long photomultiplier such as one 17 inches inlength is expensive.

(3) The photocathode employing an external photo electric effect is lowin quantum efficiency to the stimulated emission in a wavelength rangeof about 300 to 500 nm (in a blue region) and normally about 10 to 20%,whereas the quantum efficiency of the photocathode to the stimulatinglight in a wavelength range of about 600 to 700 nm (in a red region) isrelatively high and normally about 0.1 to 2%. Accordingly, a specialstimulating light cut filter is required to a sufficient S/N ratio,which adds to the cost.

(4) The photomultiplier comprises a complicated multistage dynode, andaccordingly it is difficult to make a line sensor which is large inwidth, e.g., 17 inches, and is as small as about 100 μm in pictureelement size.

From the viewpoint of shortening the stimulated emission reading time,reduction of the size of the system and reduction of the manufacturingcost of the system, there have been proposed, for instance, in JapaneseUnexamined Patent Publication No. 60(1985)-111568, an image read-outmethod and system in which a line stimulating light source such as afluorescent lamp, a cold cathode fluorescent lamp, or a LED array whichprojects a line beam onto the stimulable phosphor sheet, a line sensorhaving a solid photoelectric convertor element array extending in thedirection of length of the portion of the stimulable phosphor sheetexposed to the line beam and a scanning means which moves the linesource and the line sensor relatively to the stimulable phosphor sheetin a sub-scanning direction substantially perpendicular to the portionof the stimulable phosphor sheet exposed to the line beam are employed,and stimulated emission emitted from parts of the stimulable phosphorsheet exposed to the line beam is read in sequence while moving the linesource and the line sensor relatively to the stimulable phosphor sheetin the sub-scanning direction.

In the above identified Japanese patent publication, there is disclosed,as the solid photoelectric convertor element for forming the linesensor, a photoconductor including those whose band gaps E are eitherlarger or smaller than energy of photons hc/λ at the wavelength λ of thestimulating light (E>hc/λ, or E<hc/λ). Those whose band gaps E arelarger than energy of photons hc/λ at the wavelength λ of thestimulating light include, for instance, ZnS, ZnSe, CdS, TiO₂ and ZnO,and those whose band gaps E are smaller than energy of photons hc/λ atthe wavelength k of the stimulating light include, for instance, a-SiH,CdS(Cu), ZnS(Al), CdSe and PbO, a-representing “amorphous”. Further, ithas been proposed to use a line sensor formed of Si photodiodes.

However, use of a line sensor formed of the materials described abovegives rise to the following problems. That is, though it is advantageousthat the solid photoelectric convertor element itself has electronmultiplying function since the stimulated emission is very weak, any oneof the line sensors formed of the materials described above except theSi photodiode exhibits no avalanche amplification effect as the electronmultiplying function. On the other hand, the line sensor of the Siphotodiode is very low (substantially zero) in quantum efficiency(sensitivity) to light in an ultraviolet to blue region and is high inquantum efficiency (sensitivity) to light in a red region, which resultsin a poor blue/red sensitivity ratio. Further since being large in darkcurrent, the line sensor of the Si photodiode is not sufficient todetect weak stimulated emission in a blue region, and accordingly, anobtained image is very low in S/N ratio and in quality. Further, when along line sensor such as of 17 inches is made of Si photodiode, the linesensor becomes very expensive. Further since the stimulated emission isvery weak, it is necessary for the photoconductive material layer to bevery high in dark resistance. However, the photoconductive materialdescribed above are all low in dark resistance and accordingly read-outmust be effected with a relatively high electric field applied to thephotoconductive material layer, which increases the dark current andmakes it difficult to obtain a high S/N ratio.

Further there has been proposed, for instance, in Japanese UnexaminedPatent Publication No. 60(1985)-236354, an image read-out method andsystem in which a stimulating light source which emits a spot light suchas a laser beam, and a scanning optical system which moves the spotlight and a line sensor relatively to the stimulable phosphor sheet in asub-scanning direction are employed, and stimulated emission emittedfrom parts of the stimulable phosphor sheet exposed to the light spot isread in sequence while moving the stimulating light source and the linesensor relatively to the stimulable phosphor sheet in the sub-scanningdirection. However the solid photoelectric convertor element forming theline sensor in this method and system is the same as that used inJapanese Unexamined Patent Publication No. 60(1985)-111568 andaccordingly gives rise to the same problems.

In “RADIOGRAPHIC PROCESS UTILIZING A PHOTOCONDUCTIVE SOLID-STATE IMAGE”(772/Research disclosure, October 1992/34264), Japanese PatentPublication No. 7(1995)-76800 and Japanese Unexamined Patent PublicationNo. 58(1983)-121874, there is disclosed an image read-out system inwhich a stimulable phosphor sheet and a radiation image conversion panelwhich is substantially the same in area as the stimulable phosphorsheet, comprises a photoconductor material layer having sensitivity tothe stimulated emission and sandwiched between a pair of electrodelayers, and functions as a zero-dimensional photoelectric convertor areused and an image is read out while scanning the radiation imageconversion panel with a spot light.

It is said that the photoconductor material layer is preferably of aphotoconductive material which is high in sensitivity to the stimulatedemission in a wavelength range of about 300 to 500 nm and low insensitivity to the stimulating light in a wavelength range of about 600to 800 nm. It is said that a preferable photoconductive materialincludes selenium compounds and amorphous (a-Se) is especiallypreferred.

However, use of selenium compound as the photoconductive material givesrise to the following problem. That is, though it is advantageous thatthe solid photoelectric convertor element itself has electronmultiplying function since the stimulated emission is very weak, the S/Nratio cannot be high so long as the selenium compound has not electronmultiplying function (the above identified references make no mention ofwhether the selenium compound has electron multiplying function). Theselenium compound such as a-Se is not generally used for electronmultiplication unlike the photomultiplier.

In “RADIOGRAPHIC PROCESS UTILIZING A PHOTOCONDUCTIVE SOLID-STATE IMAGE”(772/Research disclosure, October 1992/34264) (will be referred to as“reference 1”, hereinbelow), there is disclosed an image read-out systemin which a stimulable phosphor sheet and a radiation image conversionpanel which is substantially the same in area as the stimulable phosphorsheet, comprises a photoconductor material layer having sensitivity tothe stimulated emission and sandwiched between a pair of electrodelayers, and functions as a zero-dimensional photoelectric convertor areused and an image is read out while scanning the radiation imageconversion panel with a spot light.

It is said that the photoconductor material layer is preferably of aphotoconductive material which is high in sensitivity to the stimulatedemission at 500 nm and low in sensitivity to the stimulating light at633 nm. It is said that amorphous (a-Se) is especially preferable as thephotoconductive material layer.

Since a-Se is highly sensitive to light not longer than 500 nm (e.g., ablue region from 300 to 500 nm) and is higher than a photomultiplier (asa zero-dimensional photoelectric convertor) in quantum efficiency tostimulated emission near 400 nm, a-Se is suitable for detectingstimulated emission emitted from the stimulable phosphor layer. Furthersince a-Se is hardly sensitive to light not shorter than 600 nm (e.g., ared region from 600 to 800 nm), and is large in the sensitivity tostimulated emission/sensitivity to stimulating light ratio, the a-Sephotoconductive material layer can detect the stimulated emissionemitted from the stimulable phosphor layer without use of stimulatinglight cut filter. Further, an a-Se layer can be formed bylow-temperature deposition process, and is suitable for forming a solidimage sensor which is thin, large in area and strong to impact.

However, when a radiation image conversion panel which is substantiallythe same in area as the stimulable phosphor sheet is formed of a-Se, thearea of the photoconductive material layer becomes very large, whichresults in generation of an excessive dark current and a largecapacitance (output capacity of detector), and the S/N ratiodeteriorates.

Further, since it takes a long time for stimulated emission to beemitted from the stimulable phosphor layer upon exposure to thestimulating light, when the stimulable phosphor sheet istwo-dimensionally scanned with stimulating light in the form of a spotbeam, it takes a long time to read out image from the stimulablephosphor sheet.

Further, also in Japanese Patent Publication No. 7(1995)-76800 (will bereferred to as “reference 2”, hereinbelow), it is disclosed thatstimulated emission emitted from a stimulable phosphor layer is detectedby a photoconductive material layer which is substantially the same inarea as the stimulable phosphor sheet. It is said that thephotoconductor material layer is preferably of a photoconductivematerial which is high in sensitivity to the stimulated emission in awavelength range of about 300 to 500 nm and low in sensitivity to thestimulating light in a wavelength range of about 600 to 800 nm. It issaid that selenium compounds are especially preferable as the materialof the photoconductive material layer. It is further said that influenceof a dark current can be suppressed by dividing a part of the electrodesinto a plurality of electrode elements and detecting electric currentsseparately from the electrode elements.

However even if the electrode is so divided, the area of each electrodeelement is still large, and accordingly generation of an excessive darkcurrent cannot be avoided and the capacitance is still large, whichresults in deterioration of the S/N ratio. Further, even if an imagesignal is read out by scanning the electrode elements with a spot beam,the read-out speed cannot be substantially increased.

Further also in Japanese Unexamined Patent Publication No.58(1983)-121874 (will be referred to as “reference 3”, hereinbelow), itis disclosed that stimulated emission emitted from a stimulable phosphorlayer is detected by a photoconductive material layer which issubstantially the same in area as the stimulable phosphor sheet and thephotoconductive material layer is formed selenium compounds. It isfurther disclosed that influence of a dark current can be suppressed bydividing a part of the electrodes into a plurality of electrode elementsand detecting electric currents separately from the electrode elements.Further, the reference 3 further says that when the capacitance of thephotoconductive material layer is large and additional noise isgenerated, the additional noise can be suppressed by dividing theelectrode into a plurality of parallel stripe electrode elements.

However, even if the electrode is so divided, the electrode elements arenot in one-to-one correspondence with the picture elements and signalread-out is not effected line by line. Accordingly, the read-out speedcannot be substantially increased. Further even if the electrode is sodivided, so long as the pre-amplifiers such as current detectingamplifiers as a means for reading out the charges generated in thephotoconductive material layer and obtaining an image signal are in theform of charge amplifiers, the output capacity itself forms a noisesource. Further when the pre-amplifiers are of a current-voltageconversion system (including a logarithmic amplifier), it is difficultto ensure stability. In other words, it is difficult to obtain a highspeed circuit. Further, not only the dark current but also residualelectric charges can produce false signals or flare.

Further, there has been known a system in which “preliminary read-out”is effected prior to “final read-out” in order to ascertain thecharacteristics of the radiation image stored on the stimulable phosphorsheet such as the dynamic range of the radiation image. The preliminaryread-out is carried out by use of stimulating light having stimulationenergy of a level lower than the stimulation level of stimulating lightused in the final read-out. On the basis of the preliminary read-outimage signal obtained by the preliminary read-out, read-out conditionsand/or image processing conditions for final read-out are determined.

Further we have proposed a method of determining the read-out conditionsand/or image processing conditions for final read-out without carryingout such preliminary read-out. See Japanese Unexamined PatentPublication Nos. 55(1980)-48672, 55(1980)-50180, 56(1981)-11348, and thelike. In this method, momentary light emitted from the stimulablephosphor sheet upon exposure to the recording radiation is detected byan exclusive detector such as a photo-timer, and information on thecharacteristic of the radiation image stored on the stimulable phosphorsheet, the amount of radiation stored on the stimulable phosphor sheetand the like is obtained on the basis of the detected momentary light,and the read-out conditions and the like are determined on the basis ofthe information.

The level of the stimulation energy means the total amount ofstimulation energy to which the stimulable phosphor sheet is exposed(the amount of stimulation energy per unit time×time). In order to lowerthe level of the stimulation energy, exposed dose of the stimulatinglight is reduced, or the scanning speed is increased so that the numberof picture elements becomes smaller as compared with the final read-out.

The read-out conditions are various conditions which affect the relationbetween the amount of stimulated emission and the output of the read-outsystem. The read-out conditions include, for instance, the read-out gainwhich governs the relation between input and output, the scale factorand the power of the stimulating light for read-out.

The image processing conditions are various conditions for carrying outprocessing which affects gradation, sensitivity and the like of an imagereproduced on the basis of the image signal. In systems where theaforesaid preliminary read-out is not carried out, the image processingconditions include also the aforesaid read-out gain and the scalefactor.

The method of determining optimal image processing conditions is appliedto not only the system using the stimulable phosphor sheet but also thesystem in which an image signal is obtained from a recording medium suchas X-ray film. The system for determining the read-out/conditions and/orthe image processing conditions sometimes called an EDR processingsystem.

However, when the preliminary read-out is carried out by use of a lowlevel stimulating light, the amount of information to be obtained by thefinal read-out is reduced by the amount of stimulated emission emittedfrom the stimulable phosphor sheet upon exposure to the preliminaryread-out stimulating light, and accordingly, the image signal obtainedsomewhat deteriorates in the S/N ratio as compared with that obtainedwithout carrying out preliminary read-out. Further, scanning thestimulating light beam for the preliminary read-out adds to the imageread-out time.

On the other hand, when the image read-out conditions and/or the imageprocessing conditions are determined by detecting momentary lightemitted from the stimulable phosphor sheet upon exposure to therecording radiation by an exclusive detector such as a photo-timer, useof the exclusive detector adds to the cost. Further there is a problemthat since the detector such as the photo-timer is generally narrow indetecting area and limited in measuring range, the conditions cannot beset at a high accuracy.

SUMMARY OF THE INVENTION

In view of the foregoing observations and description, the primaryobject of the present invention is to provide an image read-out methodand system which can detect at a high efficiency stimulated emission ina blue region emitted from a stimulable phosphor sheet and can read outan image at a high S/N ratio.

Another object of the present invention is to provide an image read-outmethod and system

In accordance with a first aspect of the present invention, there isprovided an image read-out method of obtaining an image signal bearingthereon image information by use of a stimulable phosphor sheet having alayer of stimulable phosphor which emits stimulated emission inproportion to the stored energy of radiation upon exposure tostimulating light and a solid image sensor having a photoconductivematerial layer which exhibits electric conductivity upon exposure to thestimulated emission from the stimulable phosphor sheet and by scanningwith stimulating light a stimulable phosphor sheet which has beenexposed to radiation and has stored thereon an image, causing thephotoconductive material layer to be exposed to stimulated emissionemitted from the stimulable phosphor sheet upon exposure to thestimulating light, and detecting electric charges generated in thephotoconductive material layer upon exposure to the stimulated emissionby applying an electric field to the photoconductive material layer,wherein the improvement comprises that

said stimulable phosphor sheet has a layer of stimulable phosphor whichis stimulated by stimulating light in a wavelength range of not shorterthan 600 nm (preferably in a red region from 600 to 800 nm) and emitsstimulated emission in a wavelength range of not longer than 500 nm(preferably in a blue region from 300 to 500 nm), said solid imagesensor has a photoconductive material layer whose major component isa-Se, and said electric field is such as to generate an avalancheamplification effect in the photoconductive material layer.

The stimulable phosphor sheet and the solid image sensor may be separatemembers or may be integrated to a unit. When a relatively thinstimulable phosphor sheet and a relatively thin solid image sensor arelaminated into an image detecting sheet with the stimulable phosphorlayer and the photoconductive material layer opposed to each other, athin and light image detecting sheet can be obtained. Such an imagedetecting sheet can remarkably improve the stimulated emissioncollecting efficiency and provides a high quality image. Further whensuch a solid image sensor is employed, a photomultiplier need not beused, which makes it feasible to reduce the overall size of the system.

The solid image sensor may be in the form of a two-dimensional sensor(area sensor), a one-dimensional sensor (linear sensor) or azero-dimensional sensor (smaller in area than the area sensor or thelinear sensor).

The stimulating light which scans the stimulable phosphor sheet may bein any form, e.g., in the form of a spot beam, or a line beam.

The thickness of the photoconductive material layer of the solid imagesensor is preferably not smaller than 1 μm so that the photoconductivematerial layer absorbs a sufficient amount of stimulated emission, anavalanche amplification effect can be obtained and the level of signalto be taken out can be high enough. Further, it is preferred that thethickness of the photoconductive material layer be as large as possiblein order to reduce the distribution capacity and suppress fixed noise,but when the thickness is too large, the voltage of the power source forimparting the electric field becomes too high. Accordingly, in order toincrease the ratio of the avalanche amplification effect to the fixednoise while taking into account the voltage of the power source, thethickness of the photoconductive material layer of the solid imagesensor is preferably not smaller than 1 μm and not larger than 100 μm,and more preferably not smaller than 10 μm and not larger than 50 μm.

When a photoconductive material layer whose major component is a-Se isused under an electric field which generates an avalanche amplificationeffect in the photoconductive material layer, the photoconductivematerial layer becomes sensitive to fluctuation of electric fielddistribution (e.g., fluctuation in the voltage of the power source) andthe image signal fluctuates. Accordingly, it is preferred thatfluctuation of the image signal due to fluctuation in electric fielddistribution be suppressed. The fluctuation of the image signal can besuppressed, for instance, by suppressing fluctuation of the voltage ofthe power source, or by storing fluctuation in the output data withfluctuation in the voltage of the power source and correcting the imagesignal according to fluctuation of the voltage of the power sourceduring read-out of the image signal.

In accordance with a second aspect of the present invention, there isprovided an image read-out system comprising

a stimulating light source which emits stimulating light in a wavelengthrange of not shorter than 600 nm (preferably in a red region from 600 to800 nm),

a stimulating light scanning means which causes the stimulating lightemitted from the stimulating light source to scan a stimulable phosphorsheet having a layer of stimulable phosphor which emits stimulatedemission in a wavelength range of not longer than 500 nm (preferably ina blue region from 300 to 500 nm) in proportion to the stored energy ofradiation upon exposure to the stimulating light,

a solid image sensor having a photoconductive material layer the majorcomponent of which is a-Se and which exhibits electric conductivity uponexposure to the stimulated emission from the stimulable phosphor sheet,

an electric voltage imparting means which imparts an electric voltage tothe photoconductive material layer of the solid image sensor to applysuch an electric field as to generate an avalanche amplification effectin the photoconductive material layer, and

an image signal obtaining means which detects electric charges generatedin the photoconductive material layer of the solid image sensor when thestimulable phosphor sheet is exposed to the stimulating light andstimulated emission emitted from the stimulable phosphor sheet impingesupon the photoconductive material with an electric voltage imparted tothe photoconductive material layer by the electric voltage applicationmeans to apply such an electric field as to generate an avalancheamplification effect in the photoconductive material layer, and detectsan image signal representing an image stored on the stimulable phosphorsheet.

The thickness of the photoconductive material layer of the solid imagesensor is preferably not smaller than 1 μm and not larger than 100 μm,and more preferably not smaller than 10 μm and not larger than 50 μm.

Further, it is preferred that the image read-out system of the secondaspect be further provided with a fluctuation suppressing means whichsuppresses fluctuation of the image signal due to fluctuation in theelectric field applied to the photoconductive material layer.

In the image read-out method of the first aspect of the presentinvention and the image read-out system of the second aspect of thepresent invention, a stimulable phosphor sheet having a layer ofstimulable phosphor which is stimulated by stimulating light in awavelength range of not shorter than 600 nm and emits stimulatedemission in a wavelength range of not longer than 500 nm in proportionto the stored energy of radiation upon exposure to the stimulatinglight, and a solid image sensor having a photoconductive material layerthe major component of which is a-Se and which exhibits electricconductivity upon exposure to the stimulated emission from thestimulable phosphor sheet are employed in combination with each other,and the image stored on the stimulable phosphor sheet is read out whileapplying, to the photoconductive material layer, such an electric fieldas to generate an avalanche amplification effect in the photoconductivematerial layer. a-Se is high in sensitivity to a wavelength in a blueregion not longer than 500 nm and the quantum efficiency of a-Se tostimulated emission close to 400 nm is as high as 60 to 70%.Accordingly, in accordance with the method and system of the first andsecond aspects, stimulated emission in a blue region emitted from thestimulable phosphor sheet can be detected at a high efficiency. Further,by virtue of the avalanche amplification effect, the amount of chargesto be taken out can be greatly increased, whereby the S/N ratio of theimage signal can be improved and the quality of the image can beimproved.

Further when fluctuation of the image signal due to fluctuation inelectric field distribution is suppressed, a stable image signal isobtained and an image of higher quality can be obtained.

Further since a-Se hardly has sensitivity to light in a wavelength rangenot shorter than 600 nm and almost wholly transmits such light, a-Se islarge in the ratio of the sensitivity to the stimulated emission (near400 nm) to that to the stimulating light (600 to 700 nm). For example,in a state where no avalanche amplification effect is obtained, theratio of the sensitivity to blue light (470 nm) to that to red light(680 nm) is about 3.5 when the thickness of the a-Se layer is 10 μm. Asthe thickness of the a-Se layer is smaller, the blue/red sensitivityratio increases and when an avalanche amplification effect is available,the blue/red sensitivity ratio further increases. Accordingly, use of astimulating light cut filter is basically unnecessary, and by projectingstimulating light not shorter than 600 nm in wavelength though aphotoconductive material layer of a-Se, stimulated emission emitted fromthe surface of the stimulable phosphor layer can be effectively detectedby the photoconductive material layer, whereby an image at high qualitycan be obtained. Further, since a-Se is very high in dark resistance ascompared with a Si avalanche photodiode and the like, a high S/N ratiocan be obtained.

Further when a Si avalanche photodiode is used as a solid image sensor,it is difficult to form a solid image sensor of a large area, e.g., aline sensor or an area sensor, since Si is in the form of a crystal. Tothe contrast, an a-Se layer can be formed by low-temperature depositionprocess, and is suitable for forming a solid image sensor which is thin,large in area and strong to impact. For example, a long linear sensor oran area sensor can be easily formed of a-Se.

Still another object of the present invention is to provide an imageread-out method and an image read-out system in which a radiation imageexcellent in S/N ratio can be read out at a high speed by use of a solidimage sensor or an image detecting sheet.

Still another object of the present invention is to provide a solidimage sensor and an image detecting sheet which can used to detect weakstimulated emission emitted from a stimulable phosphor sheet, and whichis small in output capacity so that a high S/N ratio can be obtained andcan greatly increase the image read-out speed.

Still another object of the present invention is to provide a solidimage sensor and an image detecting sheet which is strong againstimpact, can be thin, is higher than a photomultiplier in quantumefficiency to stimulated emission and/or sensitivity to blue/sensitivityto red ratio, large in dark resistance, can obtain a high S/N ratio, andcan be made in a large area easily and at low cost.

In accordance with a third aspect of the present invention, there isprovided an image read-out method of obtaining an image signal bearingthereon image information by use of a stimulable phosphor sheet having alayer of stimulable phosphor which emits stimulated emission inproportion to the stored energy of radiation upon exposure tostimulating light and a solid image sensor having a photoconductivematerial layer which exhibits electric conductivity upon exposure to thestimulated emission from the stimulable phosphor sheet and a pair ofelectrode layers which are disposed on opposite sides of thephotoconductive material layer and are provided with electrodes fordetecting electric charges generated in the photoconductive materiallayer, and by scanning with stimulating light a stimulable phosphorsheet which has been exposed to radiation and has stored thereon animage, causing the photoconductive material layer to be exposed tostimulated emission emitted from the stimulable phosphor sheet uponexposure to the stimulating light, and detecting electric chargesgenerated in the photoconductive material layer upon exposure to thestimulated emission by applying an electric field to the photoconductivematerial layer, wherein the improvement comprises that

said stimulable phosphor sheet has a layer of stimulable phosphor whichis stimulated by stimulating light in a wavelength range of not shorterthan 600 nm (preferably in a red region from 600 to 800 nm) and emitsstimulated emission in a wavelength range of not longer than 500 nm(preferably in a blue region from 300 to 500 nm),

said solid image sensor has a photoconductive material layer whose majorcomponent is a-Se, and

the electrode of at least one of the electrode layers is divided bypicture element pitches into a stripe electrode comprising a pluralityof line electrode elements arranged in a row.

In this specification, the expression “the electrode is divided bypicture element pitches” means that the electrode is divided into aplurality of elements which are arranged in pitches equal to the pictureelement pitches and each of which is not larger than the picture elementpitches so that each electrode element is in one-to-one correspondenceto a picture element in the direction of arrangement of the electrodeelements. An insulator member (may be said photoconductive materiallayer) is disposed in each gap between adjacent electrode elements.

In the image read-out method in accordance with the third aspect of thepresent invention, it is preferred that the stimulating light in theform of a line beam which intersects the longitudinal direction of theline electrode elements of said one electrode layer be employed, theline beam be caused to scan the solid image sensor in the longitudinaldirection of the line electrode elements of said one electrode layerwhile applying an electric field between each of the line electrodeelements of said one electrode layer and the electrode of the otherelectrode layer, and electric charges generated in the photoconductivematerial layer as the line beam scans the solid image sensor be detectedline electrode element by line electrode element.

Further it is preferred that the electrode of the other electrode layerbe divided into a stripe electrode comprising a plurality of lineelectrode elements arranged in a row, each extending to intersect theline electrode elements of said one electrode layer, and an electricfield be applied between one of the line electrode elements of said theother electrode layer corresponding to the read-out line and the lineelectrode elements of said one electrode layer.

It is further preferred that also the electrode of said the otherelectrode layer be divided by picture element pitches so that each lineelectrode element is in one-to-one correspondence to a picture elementin the direction of arrangement of the line electrode elements.

The thickness of the photoconductive material layer of the solid imagesensor is preferably not smaller than 0.1 μm so that the photoconductivematerial layer absorbs a sufficient amount of stimulated emission andthe level of signal to be taken out can be high enough. Further, it ispreferred that the thickness of the photoconductive material layer be aslarge as possible in order to reduce the distribution capacity andsuppress fixed noise, but when the thickness is too large, the voltageof the power source for imparting the electric field becomes too high.Accordingly, in order to reduce the fixed noise while taking intoaccount the voltage of the power source, the thickness of thephotoconductive material layer of the solid image sensor is preferablynot smaller than 0.1 μm and not larger than 100 μm.

Further, it the image read-out method in accordance with the thirdaspect of the present invention, it is preferred that said electricfield be such as to generate an avalanche amplification effect in thephotoconductive material layer. In order to make effective the avalancheamplification, the thickness of the photoconductive material layer ispreferably not smaller than lam and more preferably not smaller than 10μm. In order to generate the avalanche amplification effect in thephotoconductive material layer, it is necessary to apply a high electricfield to the photoconductive material layer. However, when the thicknessis too large, the voltage of the power source for imparting the electricfield becomes too high. Accordingly, in order to increase the avalancheamplification effect while taking into account the voltage of the powersource, the thickness of the photoconductive material layer of the solidimage sensor is preferably not smaller than 1 μm (more preferably notsmaller than 10 μm) and not larger than 50 μm.

When a photoconductive material layer whose major component is a-Se isused under an electric field which generates an avalanche amplificationeffect in the photoconductive material layer, the photoconductivematerial layer becomes sensitive to fluctuation of electric fielddistribution (e.g., fluctuation in the voltage of the power source) andthe image signal fluctuates. Accordingly, it is preferred thatfluctuation of the image signal due to fluctuation in electric fielddistribution be suppressed. The fluctuation of the image signal can besuppressed, for instance, by suppressing fluctuation of the voltage ofthe power source, or by storing fluctuation in the output data withfluctuation in the voltage of the power source and correcting the imagesignal according to fluctuation of the voltage of the power sourceduring read-out of the image signal.

Further it is preferred that the solid image sensor be provided with aphotoconductive material layer which also exhibits electric conductivityupon exposure to recording light bearing thereon image information ormomentary light emitted from the stimulable phosphor layer upon exposureto the recording light, and charges generated in the photoconductivematerial layer when the recording light or the momentary light impingesupon the photoconductive material layer be detected, thereby obtaining apreliminary read-out image signal. This means that a preliminaryread-out image signal is obtained by use of a solid image sensor whichis used in the final read-out. From this viewpoint, it is preferred thatthe method be applied to a system in which an image recording system andan image read-out system are integrated into a unit or to a radiationimage detecting sheet comprising a stimulable phosphor sheet having astimulable phosphor layer and a solid image sensor having aphotoconductive material layer which are integrated into a unit.

In order to obtain a more accurate preliminary read-out image signal, itis preferred that a solid image sensor in which the electrode of theother electrode layer is divided into a stripe electrode comprising aplurality of line electrode elements arranged in a row, each extendingto intersect the line electrode elements of said one electrode layer beused, and electric charges generated in the photoconductive materiallayer when the recording light or the momentary light impinges upon thephotoconductive material layer be detected by line electrode elements ofsaid the other electrode layer.

In this case, since a preliminary read-out image signal is read outthrough the line electrode elements of each of the electrode layers, amore detailed preliminary read-out image signal can be obtained from thetwo preliminary read-out image signals.

How to use the two preliminary read-out image signal depends upon theprojecting condition of the recording light. For example when the entirearea of the stimulable phosphor sheet is flashed to the recording lightat one time, one-dimensionally compressed information integrated in thelongitudinal direction of the line electrode elements of one electrodelayer is obtained from the line electrode elements of the one electrodelayer, and one-dimensionally compressed information integrated in thetransverse direction of the line electrode elements of the one electrodelayer is obtained from the line electrode elements of the electrodelayer. Then, a more detailed preliminary read-out image signal can beobtained from the two pieces of one-dimensionally compressedinformation.

In accordance with a fourth aspect of the present invention, there isprovided an image read-out system comprising

a stimulating light scanning means which causes stimulating light toscan a stimulable phosphor sheet having a stimulable phosphor layerwhich emits stimulated emission in proportion to the stored energy ofradiation upon exposure to the stimulating light,

a solid image sensor having a photoconductive material layer whichexhibits electric conductivity upon exposure to the stimulated emissionfrom the stimulable phosphor sheet and a pair of electrode layers whichare disposed on opposite sides of the photoconductive material layer andare provided with electrodes for detecting electric charges generated inthe photoconductive material layer,

an electric voltage imparting means which imparts an electric voltage tothe photoconductive material layer of the solid image sensor to apply anelectric field to the photoconductive material layer, and

an image signal obtaining means which detects electric charges generatedin the photoconductive material layer of the solid image sensor when thestimulable phosphor sheet is exposed to the stimulating light andstimulated emission emitted from the stimulable phosphor sheet impingesupon the photoconductive material with an electric voltage imparted tothe photoconductive material layer by the electric voltage applicationmeans to apply an electric field to the photoconductive material layer,and detects an image signal representing an image stored on thestimulable phosphor sheet, wherein the improvement comprises that

said stimulable phosphor sheet has a stimulable phosphor layer which isstimulated by stimulating light in a wavelength range of not shorterthan 600 nm (preferably in a red region from 600 to 800 nm) and emitsstimulated emission in a wavelength range of not longer than 500 nm(preferably in a blue region from 300 to 500 nm),

said solid image sensor has a photoconductive material layer whose majorcomponent is a-Se, and

the electrode of at least one of the electrode layers is divided bypicture element pitches into a stripe electrode comprising a pluralityof line electrode elements arranged in a row.

In the image read-out system in accordance with the fourth aspect of thepresent invention, it is preferred that

the stimulating light scanning means causes the stimulating light in theform of a line beam which intersects the longitudinal direction of theline electrode elements of said one electrode layer to scan the solidimage sensor in the longitudinal direction of the line electrodeelements of said one electrode layer,

the electric voltage imparting means imparts an electric voltage betweenthe electrode layers so that an electric field is generated in thephotoconductive material layer between each of the line electrodeelements of said one electrode layer and the electrode of the otherelectrode layer, and

the image signal obtaining means detects electric charges generated inthe photoconductive material layer as the line beam scans the solidimage sensor line electrode element by line electrode element.

Further it is preferred that the electrode of the other electrode layerbe divided into a stripe electrode comprising a plurality of lineelectrode elements arranged in a row, each extending to intersect theline electrode elements of said one electrode layer, and the electricvoltage imparting means imparts an electric voltage between theelectrode layers so that an electric field is applied to thephotoconductive material layer between one of the line electrodeelements of said the other electrode layer corresponding to the read-outline and the line electrode elements of said one electrode layer.

The thickness of the photoconductive material layer of the solid imagesensor is preferably not smaller than 0.1 μm and not larger than 100 μm.

Further, in the image read-out system in accordance with the fourthaspect of the present invention, it is preferred that said electricvoltage imparting means imparts an electric voltage which applies anelectric field such as to generate an avalanche amplification effect inthe photoconductive material layer. In this case, the thickness of thephotoconductive material layer of the solid image sensor is preferablynot smaller than 10 μm and not larger than 50 μm.

It is further preferred that the image read-out system of the fourthaspect of the present invention be provided with a fluctuationsuppressing means which suppresses fluctuation of the image signal dueto fluctuation in the electric field applied to the photoconductivematerial layer.

Further it is preferred that the solid image sensor be provided with aphotoconductive material layer which also exhibits electric conductivityupon exposure to recording light bearing thereon image information ormomentary light emitted from the stimulable phosphor layer upon exposureto the recording light, and there is provided a preliminary read-outimage signal obtaining means which obtains a preliminary read-out imagesignal bearing thereon image information by detecting charges generatedin the photoconductive material layer when the recording light or themomentary light impinges upon the photoconductive material layer.

In accordance with a fifth aspect of the present invention, there isprovided a two-dimensional solid image sensor for use in the imageread-out method and the image read-out system in accordance with thethird and fourth aspects of the present invention comprising aphotoconductive material layer which exhibits electric conductivity uponexposure to stimulated emission from a stimulable phosphor sheet and apair of electrode layers which are disposed on opposite sides of thephotoconductive material layer and are provided with electrodes fordetecting electric charges generated in the photoconductive materiallayer, wherein the improvement comprises that

said solid image sensor has a photoconductive material layer whose majorcomponent is a-Se, and

the electrode of at least one of the electrode layers is divided bypicture element pitches into a stripe electrode comprising a pluralityof line electrode elements arranged in a row.

It is preferred that the electrode of the other electrode layer bedivided into a stripe electrode comprising a plurality of line electrodeelements arranged in a row, each extending to intersect the lineelectrode elements of said one electrode layer.

The thickness of the photoconductive material layer of the solid imagesensor is preferably not smaller than 0.1 μm and not larger than 100 μm.In order to increase the avalanche amplification effect, the thicknessof the photoconductive material layer of the solid image sensor ispreferably not smaller than 10. μm and not larger than 50 μm.

The stimulable phosphor sheet and the solid image sensor may be separatemembers or may be integrated into a unit. When a relatively thinstimulable phosphor sheet and a relatively thin solid image sensor arelaminated into an image detecting sheet with the stimulable phosphorlayer and the photoconductive material layer opposed to each other, athin and light image detecting sheet can be obtained. Such an imagedetecting sheet can remarkably improve the stimulated emissioncollecting efficiency and provides a high quality image. Further whensuch an image detecting sheet is employed, a photomultiplier need not beused, which makes it feasible to reduce the overall size of the system.

In accordance with a sixth aspect of the present invention, there isprovided an image detecting sheet comprising an image recording portionhaving a stimulable phosphor layer which emits stimulated emission inproportion to stored energy of radiation upon exposure to stimulatinglight and an image read-out portion which is opposed to the imagerecording portion and comprises a photoconductive material layer whichexhibits electric conductivity upon exposure to the stimulated emissionfrom the stimulable phosphor sheet and a pair of electrode layers whichare disposed on opposite sides of the photoconductive material layer andare provided with electrodes for detecting electric charges generated inthe photoconductive material layer, wherein the improvement comprisesthat

said image recording portion has a layer of stimulable phosphor which isstimulated by stimulating light in a wavelength range of not shorterthan 600 nm (preferably in a red region from 600 to 800 nm) and emitsstimulated emission in a wavelength range of not longer than 500 nm(preferably in a blue region from 300 to 500 nm),

said image read-out portion has a photoconductive material layer whosemajor component is a-Se, and

the electrode of at least one of the electrode layers is divided bypicture element pitches into a stripe electrode comprising a pluralityof line-electrode elements arranged in a row.

It is preferred that the electrode of the other electrode layer bedivided into a stripe electrode comprising a plurality of line electrodeelements arranged in a row, each extending to intersect the lineelectrode elements of said one electrode layer.

The thickness of the photoconductive material layer of the solid imagesensor is preferably not smaller than 0.1 μm and not larger than 100 μm.In order to increase the avalanche amplification effect, the thicknessof the photoconductive material layer of the solid image sensor ispreferably not smaller than 10. μm and not larger than 50 μm.

In the image read-out method of the third aspect of the presentinvention and the image read-out system of the fourth aspect of thepresent invention, a stimulable phosphor sheet having a layer ofstimulable phosphor which is stimulated by stimulating light in awavelength range of not shorter than 600 nm and emits stimulatedemission in a wavelength range of not longer than 500 nm in proportionto the stored energy of radiation upon exposure to the stimulatinglight, and a solid image sensor having a photoconductive material layerthe major component of which is a-Se and which exhibits electricconductivity upon exposure to the stimulated emission from thestimulable phosphor sheet are employed in combination with each otherwith the electrode of at least one of the electrode layers on oppositesides of the photoconductive material layer of the solid image sensordivided by picture element pitches into a stripe electrode comprising aplurality of line electrode elements arranged in a row.

An a-Se layer is highly sensitive to a wavelength in a blue region notlonger than 500 nm (absorbs a sufficient amount of blue light) and thequantum efficiency of a-Se to stimulated emission close to 400 nm is ashigh as 60 to 70% provided that it is not smaller than 0.1 μm inthickness. Accordingly, in accordance with the method and system of thethird and fourth aspects, stimulated emission in a blue region emittedfrom the stimulable phosphor sheet can be detected at a high efficiency.Further since the electrode for detecting the charges is divided bypicture element pitches into a plurality of electrode elements so thateach electrode element is in one-to-one correspondence to a pictureelement, the area of each electrode element is very small even if thephotoconductive material layer is substantially the same as thestimulable phosphor sheet in area and, accordingly, dark current noiseand/or capacitance noise can be reduced, whereby a high quality imagewhich is high in S/N ratio can be obtained.

When electric charges are detected by the line electrode elements of theelectrode divided by picture element pitches while scanning the solidimage sensor with a line beam intersecting the longitudinal direction ofthe line electrode elements, the electric charges can be simultaneouslydetected in the direction of arrangement of the line electrode elements,which results in a higher read-out speed. Further, since a stimulatinglight source in the form of a line source can be formed by a relativelythin light source such as a fluorescent light, a LED or an organic EL,the overall system can be thin.

Further, when the electrode of the other electrode layer is divided intoa stripe electrode comprising a plurality of line electrode elementsarranged in a row, each extending to intersect the line electrodeelements of said one electrode layer, the distribution capacity can bereduced and fixed noise can be suppressed by switching the electrodeelements of said the other electrode layer with the read-out line.

Further since a-Se hardly has sensitivity to light in a wavelength rangenot shorter than 600 nm and almost wholly transmits such light, a-Se islarge in the ratio of the sensitivity to the stimulated emission (near400 nm) to that to the stimulating light (600 to 700 nm). For example,in a state where no avalanche amplification effect is obtained, theratio of the sensitivity to blue light (470 nm) to that to red light(680 nm) is about 3.5 when the thickness of the a-Se layer is 10 μm. Asthe thickness of the a-Se layer is smaller, the blue/red sensitivityratio increases and when an avalanche amplification effect is available,the blue/red sensitivity ratio further increases. Accordingly, use of astimulating light cut filter is basically unnecessary, and by projectingstimulating light not shorter than 600 nm in wavelength through aphotoconductive material layer of a-Se, stimulated emission emitted fromthe surface of the stimulable phosphor layer can be effectively detectedby the photoconductive material layer, whereby an image at high qualitycan be obtained. Further, since a-Se is very high in dark resistance ascompared with a Si avalanche photodiode and the like, a high S/N ratiocan be obtained.

Further when a Si avalanche photodiode is used as a solid image sensor,it is difficult to form a solid image sensor of a large area, e.g., anarea sensor, since Si is in the form of a crystal. To the contrast, ana-Se layer can be formed by low-temperature deposition process, and issuitable for forming a solid image sensor which is thin, large in areaand strong to impact. For example an area sensor 17″×17″ can be easilyformed of a-Se.

When an electric field which can generate an avalanche amplificationeffect is applied to the photoconductive material layer, the amount ofcharges to be taken out can be greatly increased, whereby the S/N ratioof the image signal can be improved and the quality of the image can beimproved.

Further by suppressing fluctuation in the image signal due tofluctuation in the electric field distribution, the image signal can bestabilized and the image quality is further improved.

Further, when that the solid image sensor is provided with aphotoconductive material layer which also exhibits electric conductivityupon exposure to recording light bearing thereon image information ormomentary light emitted from the stimulable phosphor layer upon exposureto the recording light, and charges generated in the photoconductivematerial layer when the recording light or the momentary light impingesupon the photoconductive material layer is detected, thereby obtaining apreliminary read-out image signal, a preliminary read-out image signalcan be obtained while a radiation image is being recorded on thestimulable phosphor sheet by use of the detecting system for finalread-out. With this arrangement, preliminary read-out does not add tothe cost.

Further, since being effected while a radiation image is being recordedon the stimulable phosphor sheet, the preliminary read-out does notreduce the amount of information to be obtained by final read-out anddoes not adversely affect the final read-out unlike preliminary read-outwhich is effected before the final read-out. Further, since it is notnecessary to scan the stimulable phosphor sheet with stimulating lightfor preliminary read-out, time loss in reading out the image can besaved. Further since preliminary read-out information on substantiallyover the entire area of the stimulable phosphor sheet can be obtained,image read-out conditions and/or the image processing conditions can beaccurately set.

In the solid image sensor in accordance with the fifth aspect of thepresent invention, the major component of the photoconductive materiallayer is a-Se and the electrode of at least one of the electrode layersis divided by picture element pitches into a stripe electrode comprisinga plurality of line electrode elements arranged in a row. Accordingly,the area of each electrode element is very small and dark current and/oroutput capacitance can be reduced.

Further in accordance with the sixth aspect of the present invention, alight and thin image detecting sheet can be obtained while keeping theaforesaid various merits. Further the stimulated emission collectingefficiency can be greatly increased and the quality of the image to beobtained can be greatly improved. Further, the radiation image recordingand read-out system can be small in size as compared with a system wherea photomultiplier is employed.

Still another object of the present invention is to provide an imageread-out method and an image read-out system for reading out a radiationimage from a stimulable phosphor sheet in which the preliminary read-outwhich is to be carried out prior to the final read-out can be carriedout accurately without affecting the final read-out and without addingto the cost.

In accordance with a seventh aspect of the present invention, there isprovided an image read-out method of obtaining an image signal bearingthereon image information by use of a stimulable phosphor sheet having alayer of stimulable phosphor which emits stimulated emission inproportion to the stored energy of radiation upon exposure tostimulating light and a solid image sensor having a photoconductivematerial layer which exhibits electric conductivity upon exposure to thestimulated emission from the stimulable phosphor sheet and by scanningwith stimulating light a stimulable phosphor sheet which has beenexposed to radiation and has stored thereon an image, causing thephotoconductive material layer to be exposed to stimulated emissionemitted from the stimulable phosphor sheet upon exposure to thestimulating light, and detecting electric charges generated in thephotoconductive material layer upon exposure to the stimulated emissionby applying an electric field to the photoconductive material layer,wherein the improvement comprises the steps of

using a solid image sensor whose photoconductive material layer alsoexhibits electric conductivity upon exposure to recording light bearingthereon image information (e.g., the radiation passing through theobject) or momentary light emitted from the stimulable phosphor layerupon exposure to the recording light,

projecting the recording light onto the stimulable phosphor sheet whileapplying an electric field to the photoconductive material layer, and

detecting charges generated in the photoconductive material layer whenthe recording light or the momentary light impinges upon thephotoconductive material layer, thereby obtaining a preliminary read-outimage signal bearing thereon image information.

This means that a preliminary read-out image signal is obtained by useof a solid image sensor which is used in the final read-out. From thisviewpoint, it is preferred that the method of the seventh aspect beapplied to a system in which an image recording system and an imageread-out system are integrated into a unit or to a two-dimensionalradiation image detecting sheet comprising a stimulable phosphor sheethaving a stimulable phosphor layer and a solid image sensor having aphotoconductive material layer which are integrated into a unit.

The solid image sensor may be a two-dimensional sensor (area sensor)which is substantially the same as the stimulable phosphor sheet inarea, or a one-dimensional sensor (line sensor) or a zero-dimensionalsensor which is long or smaller in area than the stimulable phosphorsheet. When the solid image sensor is in the form of a one-dimensionalsensor or a zero-dimensional sensor, it is preferred that thepreliminary read-out image signal be obtained by moving the solid imagesensor relatively to the stimulable phosphor sheet during exposure tothe recording light so that information on substantially the entire areaof the stimulable phosphor sheet can be obtained. In this case, thesolid image sensor may be moved at a higher speed than in the finalread-out so that a rougher preliminary read-out image signal isobtained.

When the solid image sensor is in the form of a two-dimensional sensor,in order to obtain more accurate preliminary read-out image signal, itis preferred that a solid image sensor in which the electrode of one ofthe electrode layers is divided into a stripe electrode comprising aplurality of line electrode elements arranged in a row be used, andelectric charges generated in the photoconductive material layer whenthe recording light or the momentary light impinges upon thephotoconductive material layer be detected by line electrode elements ofsaid one electrode layer.

It is further preferred that a solid image sensor in which the electrodeof the other electrode layer is also divided into a stripe electrodecomprising a plurality of line electrode elements arranged in a row,each extending to intersect the line electrode elements of said oneelectrode layer be used, and electric charges generated in thephotoconductive material layer when the recording light or the momentarylight impinges upon the photoconductive material layer be detected alsoby line electrode elements of said the other electrode layer.

In this case, since a preliminary read-out image signal is read outthrough each of the electrode layers by the line electrode elementsthereof, a more detailed preliminary read-out image signal can beobtained from the two preliminary read-out image signals.

How to use the two preliminary read-out image signal depends upon theprojecting condition of the recording light. For example when the entirearea of stimulable phosphor sheet is flashed to the recording light atone time, one-dimensionally compressed information integrated in thelongitudinal direction of the line electrode elements of one electrodelayer is obtained from the line electrode elements of the one electrodelayer, and one-dimensionally compressed information integrated in thetransverse direction of the line electrode elements of the one electrodelayer is obtained from the line electrode elements of the electrodelayer. Then, a more detailed preliminary read-out image signal can beobtained from the two pieces of one-dimensionally compressedinformation.

In accordance with an eighth aspect of the present invention, there isprovided an image read-out system comprising

a stimulating light source which emits stimulating light,

a stimulating light scanning means which causes the stimulating lightemitted from the stimulating light source to scan a stimulable phosphorsheet having a layer of stimulable phosphor which emits stimulatedemission in proportion to the stored energy of radiation upon exposureto the stimulating light,

a solid image sensor having a photoconductive material layer whichexhibits electric conductivity upon exposure to the stimulated emissionfrom the stimulable phosphor sheet,

an electric voltage imparting means which imparts an electric voltage tothe photoconductive material layer of the solid image sensor to apply anelectric field to the photoconductive material layer, and

an image signal obtaining means which detects electric charges generatedin the photoconductive material layer of the solid image sensor when thestimulable phosphor sheet is exposed to the stimulating light andstimulated emission emitted from the stimulable phosphor sheet impingesupon the photoconductive material with an electric field applied to thephotoconductive material layer, and detects an image signal representingan image stored on the stimulable phosphor sheet, wherein theimprovement comprises that

the photoconductive material layer of the solid image sensor alsoexhibits electric conductivity upon exposure to recording light bearingthereon image information or momentary light emitted from the stimulablephosphor layer upon exposure to the recording light, and

there is provided a preliminary read-out image signal obtaining meanswhich obtains a preliminary read-out image signal bearing thereon imageinformation by detecting charges generated in the photoconductivematerial layer when the recording light or the momentary light impingesupon the photoconductive material layer.

In the image read-out system in accordance with the eighth aspect of thepresent invention, it is preferred that the solid image sensor isprovided with a pair of electrode layers on opposite sides of thephotoconductive material layer, each having an electrode, the electrodeof one of the electrode layers is divided into a stripe electrodecomprising a plurality of line electrode elements arranged in a row, andthe image signal obtaining means detects electric charges generated inthe photoconductive material layer when the recording light or themomentary light impinges upon the photoconductive material layer by lineelectrode elements of said one electrode layer.

It is further preferred that the electrode of the other electrode layerbe also divided into a stripe electrode comprising a plurality of lineelectrode elements arranged in a row, each extending to intersect theline electrode elements of said one electrode layer, and the preliminaryread-out image signal obtaining means detects electric charges generatedin the photoconductive material layer when the recording light or themomentary light impinges upon the photoconductive material layer bedetected also by line electrode elements of said the other electrodelayer.

In the image read-out method in accordance with the seventh aspect ofthe present invention and the image read-out system in accordance withthe eighth aspect of the present invention, a preliminary read-out imagesignal can be obtained while a radiation image is being recorded on thestimulable phosphor sheet by use of the detecting system for finalread-out. With this arrangement, the preliminary read-out image signalcan be obtained without an additional sensor for the preliminaryread-out and accordingly, the preliminary read-out does not add to thecost.

Further, since being effected while a radiation image is being recordedon the stimulable phosphor sheet, the preliminary read-out does notreduce the amount of information to be obtained by final read-out anddoes not adversely affect the final read-out unlike preliminary read-outwhich is effected before the final read-out.

Further, since it is not necessary to scan the stimulable phosphor sheetwith stimulating light for preliminary read-out, time loss in readingout the image can be saved.

Further when a zero-dimensional or one-dimensional sensor is used,preliminary read-out information can be obtained substantially over theentire area of the stimulable phosphor sheet by moving the sensorrelatively to the stimulable phosphor sheet at a speed higher than thatfor the final read-out by use of the scanning system for the finalread-out, the read-out conditions and/or the image processing conditionscan accurately set even if the sensor itself cannot cover the entirearea of the stimulable phosphor sheet.

When a two-dimensional solid image sensor which is substantially thesame as the stimulable phosphor sheet in area is used, the preliminaryread-out can be accurately carried out by using a solid image sensorhaving a strip electrode comprising a plurality of line electrodes anddetecting the charges by the line electrodes.

Still another object of the present invention is to provide an imageread-out method and an image read-out system which can stably obtain animage excellent in S/N ratio when an image is read out by use of astimulable phosphor sheet and a solid image sensor (semiconductorsensor).

Still another object of the present invention is to provide a solidimage sensor which is used for carrying out the image read-out methodand is used in the image read-out system.

Still another object of the present invention is to provide an imageread-out method and an image read-out system which is not affected byfalse signals or flare and to provide a solid image sensor which is usedfor carrying out the image read-out method and is used in the imageread-out system.

In accordance with a ninth aspect of the present invention, there isprovided an image read-out method of obtaining an image signal bearingthereon image information by use of a stimulable phosphor sheet having alayer of stimulable phosphor which emits stimulated emission inproportion to the stored energy of radiation upon exposure tostimulating light and a solid image sensor having a photoconductivematerial layer which exhibits electric conductivity upon exposure to thestimulated emission from the stimulable phosphor sheet, and by scanningwith stimulating light a stimulable phosphor sheet which has beenexposed to radiation and has stored thereon an image, causing thephotoconductive material layer to be exposed to stimulated emissionemitted from the stimulable phosphor sheet upon exposure to thestimulating light, and detecting electric charges generated in thephotoconductive material layer upon exposure to the stimulated emission,wherein the improvement comprises that

the solid image sensor has a photoconductive material layer having anarea smaller than the area of the stimulable phosphor sheet and thestimulated emission receiving face of the solid image sensor is dividedinto a plurality of photoelectric conversion segments, and

a plurality of image signal obtaining means are discretely connected tothe respective photoelectric conversion segments to detect electriccharges generated in the photoelectric conversion segments.

The expression “the photoconductive material layer has an area smallerthan the area of the stimulable phosphor sheet” means, for instance,that one side of the photoconductive material layer is equal to orshorter than one side of the stimulable phosphor sheet and the otherside of the photoconductive material layer is shorter than the otherside of the stimulable phosphor sheet. For example, when the solid imagesensor is an elongated rectangular sensor, the long side of the solidimage sensor (for instance, along the main scanning line) may be equalto the width of the stimulable phosphor sheet, but in such a case, theshorter side of the solid image sensor should be shorter than the lengthof the stimulable phosphor sheet. Further, when the solid image sensoris substantially square in shape, each side of the solid image sensormay be smaller than the shorter side of the stimulable phosphor sheet.

Each of the photoelectric conversion segments of the solid image sensormay be different from each in size and need not be in one-to-onecorrespondence to a picture element. Further, the stimulated emissionreceiving face of the solid image sensor may be divided in either of themain scanning direction and the sub-scanning direction or may be dividedin both the main scanning direction and the sub-scanning direction.Further, the expression “the stimulated emission receiving face of thesolid image sensor is divided into a plurality of photoelectricconversion segments” means that the photoelectric conversion segmentscan function independently of each other, and the stimulated emissionreceiving face of the solid image sensor may be divided into a pluralityof photoelectric conversion segments, for instance, by dividing at leastone of the electrodes on opposite sides of the photoconductive materiallayer or by forming partition walls between the segments.

At the boundaries of the photoelectric conversion segments, stimulatedemission from one picture element can simultaneously impinge upon twophotoelectric conversion segments, and accordingly, it is preferred thatthe image signal for the one picture element be obtained by adding twoimage signals obtained from two image signal obtaining means connectedto the two photoelectric conversion segments in order to smoothen jointsof the image signals.

Further since the stimulated emission is emitted from the part of thestimulable phosphor sheet exposed to the stimulating light, thephotoelectric conversion segments upon which stimulated emission fromone picture element impinges changes with the scanning position of thestimulating light. Accordingly, it is preferred that the image signalsfrom the image signal obtaining means which are to be added be switchedin response to scanning of the stimulating light.

In accordance with a tenth aspect of the present invention, there isprovided an image read-out method of obtaining an image signal bearingthereon image information by use of a stimulable phosphor sheet having alayer of stimulable phosphor which emits stimulated emission inproportion to the stored energy of radiation upon exposure tostimulating light and a solid image sensor having a photoconductivematerial layer which exhibits electric conductivity upon exposure to thestimulated emission from the stimulable phosphor sheet, and by scanningwith stimulating light a stimulable phosphor sheet which has beenexposed to radiation and has stored thereon an image, causing thephotoconductive material layer to be exposed to stimulated emissionemitted from the stimulable phosphor sheet upon exposure to thestimulating light, and detecting electric charges generated in thephotoconductive material layer upon exposure to the stimulated emissionby applying an electric field to the photoconductive-material layer,wherein the improvement comprises that

a solid image sensor whose photoconductive material layer has an areasmaller than the area of the stimulable phosphor sheet and whosestimulated emission receiving face is divided into a plurality ofphotoelectric conversion segments is used, and

the photoelectric conversion segments are made active or inactiveindependently of each other.

The photoelectric conversion segments can be made active or inactive,for instance, by controlling application of the electric field to thephotoconductive material layer.

Since the stimulated emission is emitted from the part of the stimulablephosphor sheet exposed to the stimulating light, the photoelectricconversion segments to be effective to obtain an image signal changeswith the scanning position of the stimulating light. Accordingly, it ispreferred that making active or inactive the photoelectric conversionsegment be controlled in response to scanning of the stimulating light.

As in the method in accordance with the ninth aspect of the presentinvention, at the boundaries of the photoelectric conversion segments,stimulated emission from one picture element can simultaneously impingeupon two photoelectric conversion segments, and accordingly, it ispreferred that the image signal for the one picture element be obtainedby adding two image signals obtained from two image signal obtainingmeans connected to the two photoelectric conversion segments in order tosmoothen joints of the image signals.

Further since the stimulated emission is emitted from the part of thestimulable phosphor sheet exposed to the stimulating light, thephotoelectric conversion segments upon which stimulated emission fromone picture element impinges changes with the scanning position of thestimulating light. Accordingly, it is preferred that the output signalsfrom the photoelectric conversion segments which are to be added beswitched in response to scanning of the stimulating light.

That is, in the method in accordance with the ninth aspect of thepresent invention, the image signals are obtained by the image signalobtaining means on the basis of the output signals from thecorresponding photoelectric conversion segments and then the imagesignals are added. To the contrast, in the method in accordance with thetenth aspect of the present invention, the output signals from thecorresponding photoelectric conversion segments are added.

In the methods in accordance with the ninth and tenth aspects of thepresent invention, it is preferred that a stimulable phosphor sheethaving a layer of stimulable phosphor which is stimulated by stimulatinglight in a wavelength range of not shorter than 600 nm and emitsstimulated emission in a wavelength range of not longer than 500 nm beused, and a solid image sensor having a photoconductive material layerwhose major component is a-Se be used.

In accordance with an eleventh aspect of the present invention, there isprovided a system for carrying out the image processing method inaccordance with the ninth aspect of the present invention. That is, inaccordance with the eleventh aspect of the present invention, there isprovided an image read-out system comprising

a stimulating light source which emits stimulating light,

a stimulating light scanning means which causes the stimulating lightemitted from the stimulating light source to scan a stimulable phosphorsheet having a layer of stimulable phosphor which emits stimulatedemission in proportion to the stored energy of radiation upon exposureto the stimulating light,

a solid image sensor having a photoconductive material layer whichexhibits electric conductivity upon exposure to the stimulated emissionfrom the stimulable phosphor sheet, and

an image signal obtaining means which detects electric charges generatedin the photoconductive material layer of the solid image sensor when thestimulable phosphor sheet is exposed to the stimulating light andstimulated emission emitted from the stimulable phosphor sheet impingesupon the photoconductive material, and obtains an image signalrepresenting an image stored on the stimulable phosphor sheet, whereinthe improvement comprises that

the solid image sensor has a photoconductive material layer having anarea smaller than the area of the stimulable phosphor sheet and thestimulated emission receiving face of the solid image sensor is dividedinto a plurality of photoelectric conversion segments, and

a plurality of image signal obtaining means are discretely connected tothe respective photoelectric conversion segments.

It is preferred that the image read-out system further comprises anadder means which obtains an image signal for one picture element byadding a plurality of image signals obtained from a plurality of imagesignal obtaining means connected to a plurality of photoelectricconversion segments which receive stimulated emission from the pictureelement.

In this case, it is preferred that the image read-out system furthercomprises a switching means which switches the image signals from theimage signal obtaining means which are to be added in response toscanning of the stimulating light.

In accordance with a twelfth aspect of the present invention, there isprovided a system for carrying out the image processing method inaccordance with the tenth aspect of the present invention. That is, inaccordance with the twelfth aspect of the present invention, there isprovided an image read-out system comprising

a stimulating light source which emits stimulating light,

a stimulating light scanning means which causes the stimulating lightemitted from the stimulating light source to scan a stimulable phosphorsheet having a layer of stimulable phosphor which emits stimulatedemission in proportion to the stored energy of radiation upon exposureto the stimulating light,

a solid image sensor having a photoconductive material layer whichexhibits electric conductivity upon exposure to the stimulated emissionfrom the stimulable phosphor sheet,

an electric voltage imparting means which imparts an electric voltage tothe photoconductive material layer of the solid image sensor to apply anelectric field to the photoconductive material layer and

an image signal obtaining means which detects electric charges generatedin the photoconductive material layer of the solid image sensor when thestimulable phosphor sheet is exposed to the stimulating light andstimulated emission emitted from the stimulable phosphor sheet impingesupon the photoconductive material with an electric field applied to thephotoconductive material layer, and obtains an image signal representingan image stored on the stimulable phosphor sheet, wherein theimprovement comprises that

the solid image sensor has a photoconductive material layer having anarea smaller than the area of the stimulable phosphor sheet and thestimulated emission receiving face of the solid image sensor is dividedinto a plurality of photoelectric conversion segments, and

there is provided a control means which makes active or inactive thephotoelectric conversion segments independently of each other.

The control means may make active or inactive the photoelectricconversion segments by controlling application of the electric field tothe photoconductive material layer.

It is preferred that the control means makes active or inactive thephotoelectric conversion segments in response to scanning of thestimulating light.

It is preferred that the image read-out system further comprises anadder means which obtains an image signal for one picture element byadding a plurality of output signals from a plurality of photoelectricconversion segments which receive stimulated emission from the pictureelement.

In this case, it is preferred that the image read-out system furthercomprises a switching means which switches the output signals from thephotoelectric conversion segments which are to be added in response toscanning of the stimulating light.

In the systems in accordance with the eleventh and twelfth aspects ofthe present invention, it is preferred that the stimulable phosphorsheet has a layer of stimulable phosphor which is stimulated bystimulating light in a wavelength range of not shorter than 600 nm andemits stimulated emission in a wavelength range of not longer than 500nm, and the solid image sensor has a photoconductive material layerwhose major component is a-Se.

In accordance with a thirteenth aspect of the present invention, thereis provided a solid image sensor comprising a photoconductive materiallayer which exhibits electric conductivity upon exposure to stimulatedemission emitted from a stimulable phosphor sheet upon exposure tostimulating light, wherein the improvement comprises that

the photoconductive material layer has an area smaller than the area ofthe stimulable phosphor sheet and the stimulated emission receiving faceof the solid image sensor is divided into a plurality of photoelectricconversion segments.

It is preferred that the major component of the photoconductive materiallayer is a-Se.

In the image read-out method in accordance with the ninth aspect of thepresent invention and the image read-out system in accordance with theeleventh aspect of the present invention, since the solid image sensorhas a photoconductive material layer having an area smaller than thearea of the stimulable phosphor sheet, and the stimulated emissionreceiving face of the solid image sensor is divided into a plurality ofphotoelectric conversion segments, and a plurality of image signalobtaining means are discretely connected to the respective photoelectricconversion segments to detect electric charges generated in thephotoelectric conversion segments, each sensor is small in size andaccordingly, generation of the dark current can be suppressed and thecapacitance can be reduced, whereby the S/N ratio can be improved and ahigh quality image can be obtained.

When an image signal for one picture element is obtained by adding aplurality of image signals obtained from a plurality of image signalobtaining means connected to a plurality of photoelectric conversionsegments which receive stimulated emission from the picture element, anadverse influence of dividing the photoconductive material layer can beavoided.

Further when the image signals from the image signal obtaining meanswhich are to be added are switched in response to scanning of thestimulating light, joints of the image can be smooth.

In the image read-out method in accordance with the tenth aspect of thepresent invention and the image read-out system in accordance with thetwelfth aspect of the present invention, since the solid image sensorhas a photoconductive material layer having an area smaller than thearea of the stimulable phosphor sheet, and the stimulated emissionreceiving face of the solid image sensor is divided into a plurality ofphotoelectric conversion segments, and there is provided a control meanswhich makes active or inactive the photoelectric conversion segmentsindependently of each other, only photoelectric conversion segmentswhich are effective in reading out the image signal can be made activewhile the other photoelectric conversion segments kept inactive, wherebyinfluence of the dark current in the sensor and/or false signals due toresidual charges can be suppressed, influence of flare can be avoidedand the S/N ratio can be greatly improved. This effect cannot beobtained by simply dividing the photoelectric convertor means, forinstance, by dividing the electrode.

When the control is effected in response to the scanning position of thestimulating light, adverse influence of the control can be avoided.

When an image signal for one picture element is obtained by adding aplurality of output signals from a plurality of photoelectric conversionsegments which receive stimulated emission from the picture element, anadverse influence of the control and dividing the photoconductivematerial layer can be avoided.

Further when the output signals from the photoelectric conversionsegments which are to be added are switched in response to scanning ofthe stimulating light, joints of the image can be smooth withoutaffected by switching of the controls.

When a stimulable phosphor sheet having a layer of stimulable phosphorwhich is stimulated by stimulating light in a wavelength range of notshorter than 600 nm and emits stimulated emission in a wavelength rangeof not longer than 500 nm in proportion to the stored energy ofradiation upon exposure to the stimulating light, and a solid imagesensor having a photoconductive material layer the major component ofwhich is a-Se are employed in combination with each other, since a-Se ishigh in sensitivity to a wavelength in a blue region not longer than 500nm and the quantum efficiency of a-Se to stimulated emission close to400 nm is as high as 60 to 70%, stimulated emission in a blue regionemitted from the stimulable phosphor sheet can be detected at a highefficiency, whereby the S/N ratio of the image signal can be furtherimproved and the quality of the image can be further improved.

Further since a-Se hardly has sensitivity to light in a wavelength rangenot shorter than 600 nm and almost wholly transmits such light, a-Se islarge in the ratio of the sensitivity to the stimulated emission (near400 nm) to that to the stimulating light (600 to 700 nm). For example,in a state where no avalanche amplification effect is obtained, theratio of the sensitivity to blue light (470 nm) to that to red light(680 nm) is about 3.5 when the thickness of the a-Se layer is 10 μm. Asthe thickness of the a-Se layer is smaller, the blue/red sensitivityratio increases and when an avalanche amplification effect is available,the blue/red sensitivity ratio further increases. Accordingly, use of astimulating light cut filter is basically unnecessary, and by projectingstimulating light not shorter than 600 nm in wavelength through aphotoconductive material layer of a-Se, stimulated emission emitted fromthe surface of the stimulable phosphor layer can be effectively detectedby the photoconductive material layer, whereby an image at high qualitycan be obtained. Further, since a-Se is very high in dark resistance ascompared with a Si avalanche photodiode and the like, a high S/N ratiocan be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic perspective showing a radiation image detectingsheet in accordance with a first embodiment of the present invention,

FIG. 1B is a X-Y cross-sectional view of a part of the radiation imagedetecting sheet indicated by arrow P in FIG. 1A,

FIG. 1C a X-Z cross-sectional view of a part of the radiation imagedetecting sheet indicated by arrow Q in FIG. 1A,

FIG. 2 is a schematic view showing a radiation image recording andread-out system using the radiation image detecting sheet of the firstembodiment with the radiation image detecting sheet shown in aperspective view,

FIG. 3 is a schematic view showing the radiation image recording andread-out system with the radiation image detecting sheet shown in a X-Zcross-sectional view of the part indicated by arrow Q in FIG. 1,

FIG. 4 is a timing chart for illustrating a method of recording aradiation image and reading out the same by use of the radiation imagedetecting sheet of the first embodiment,

FIG. 5 is a schematic view showing a modification of the radiation imagerecording and read-out system shown in FIGS. 3 and 4 which is suitablefor the preliminary read-out,

FIG. 6 is a schematic X-Z cross-sectional view showing a radiation imagedetecting sheet in accordance with a second embodiment of the presentinvention,

FIG. 7 is a schematic X-Z cross-sectional view showing a radiation imagedetecting sheet in accordance with a third embodiment of the presentinvention,

FIG. 8A is a schematic perspective showing a radiation image detectingsheet in accordance with a fourth embodiment of the present invention,

FIG. 8B is a X-Y cross-sectional view of a part of the radiation imagedetecting sheet indicated by arrow P in FIG. 8A,

FIG. 8C is a X-Z cross-sectional view of a part of the radiation imagedetecting sheet indicated by arrow Q in FIG. 8A,

FIG. 9A is a schematic perspective showing a radiation image detectingsheet in accordance with a fifth embodiment of the present invention,

FIG. 9B is a X-Y cross-sectional view of a part of the radiation imagedetecting sheet indicated by arrow P in FIG. 9A,

FIG. 9C is a X-Z cross-sectional view of a part of the radiation imagedetecting sheet indicated by arrow Q in FIG. 9A,

FIG. 10 is a schematic view showing a radiation image recording andread-out system using the radiation image detecting sheet of the fifthembodiment,

FIG. 11A is a schematic perspective view showing a radiation imageread-out system in accordance with a sixth embodiment of the presentinvention,

FIG. 11B is a fragmentary cross-sectional view showing the solid imagesensor employed in the radiation image read-out system in accordancewith the sixth embodiment of the present invention,

FIG. 12A is a schematic perspective view showing a radiation imageread-out system in accordance with a seventh embodiment of the presentinvention,

FIG. 12B is a fragmentary cross-sectional view taken along line I—I inFIG. 12A,

FIG. 13A is a cross-sectional view showing the solid image sensoremployed in the radiation image read-out system in accordance with theseventh embodiment of the present invention,

FIG. 13B is a view showing a modification of the solid image sensor,

FIGS. 14A to 14C are views for illustrating various methods of using thesolid image sensor,

FIG. 15 is a schematic side view showing a modification of the solidimage sensor,

FIG. 16A is a cross-sectional view taken along the main scanning line ofa solid image sensor in accordance with an eighth embodiment of thepresent invention which is in the form of a line sensor,

FIG. 16B is a horizontal cross-sectional view showing an electrode ofthe solid image sensor shown in FIG. 16A,

FIG. 17A is a cross-sectional view taken along the main scanning line ofa solid image sensor in accordance with ninth embodiment of the presentinvention which is in the form of a line sensor,

FIG. 17B is a horizontal cross-sectional view showing an electrode ofthe solid image sensor shown in FIG. 17A,

FIGS. 18A to 18D are views showing various examples of using the solidimage sensor in the form of a line sensor,

FIGS. 19A to 19B are views showing examples of using the solid imagesensor in the form of a line sensor having a pair of arrays of solidimage sensor elements,

FIG. 20A is a schematic perspective view showing a radiation imageread-out system in accordance with a tenth embodiment of the presentinvention,

FIG. 20B is a fragmentary cross-sectional view taken along line I—I inFIG. 20A,

FIG. 21A is a cross-sectional view taken along the sub-scanning line ofthe solid image sensor employed in the radiation image read-out systemof the tenth embodiment,

FIG. 21B is a cross-sectional view taken along the main-scanning line ofthe solid image sensor,

FIG. 21C is a horizontal cross-sectional view of the solid image sensorshowing the divided electrode thereof,

FIGS. 22A to 22C are views for illustrating various ways of dividing theelectrode,

FIG. 23 is a block diagram showing a circuit for reading out an imagesignal from the solid image sensor when the electrode is divided in themanner shown in FIG. 22A,

FIG. 24A is a block diagram showing in detail a part of the circuitshown in FIG. 23,

FIG. 24B is a,view for illustrating the operation of the circuit shownin FIG. 24A when the electrode is divided in the manner shown in FIG.22A,

FIG. 25 is a view for illustrating the operation of the circuit shown inFIG. 24A when the electrode is divided in the manner shown in FIG. 22B,

FIG. 26A is a cross-sectional view taken along the sub-scanning line ofthe solid image sensor employed in the radiation image read-out systemof the eleventh embodiment,

FIG. 26B is a-cross-sectional view taken along the main-scanning line ofthe solid image sensor,

FIG. 26C is a horizontal cross-sectional view of the solid image sensorshowing the divided electrode thereof, and

FIG. 27 is a block diagram showing a part of the circuit for obtainingan image signal in the radiation image read-out system of the eleventhembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1A to 1C, a radiation image detecting sheet 1 inaccordance with a first embodiment of the present invention comprises animage recording portion (a stimulable phosphor sheet) 10 and an imageread-out portion (a solid image sensor) 20. The image recording portion10 is formed by forming on a base 11 a stimulable phosphor layer 12which emits stimulated emission in proportion to radiation energy storedthereon upon exposure to stimulating light. The image read-out portion20 comprises a first electrode layer 21, a photoconductive materiallayer 23 which exhibits electric conductivity upon exposure tostimulated emission from the stimulable phosphor layer 12, and a secondelectrode layer 25 superposed one on another in this order. The firstelectrode layer 21 is formed of a first stripe electrode 22 comprising aplurality of linear electrode elements 22 a spaced from each other withgaps 21 a interposed between the elements 22 a, and the second electrodelayer 25 is formed of a second stripe electrode 26 comprising aplurality of linear electrode elements 26 a spaced from each other withgaps 25 a interposed between the elements 26 a. The image recordingportion 10 and the image read-out portion 20 are superposed with thestimulable phosphor layer 12 and the second electrode layer 25 facingeach other.

The image recording portion 10 may be of any form so long as thestimulable phosphor layer 12 is stimulated by red stimulating light in awavelength range of not shorter than 600 nm and emits stimulatedemission in a wavelength range of not longer than 500 nm (preferablyfrom 400 to 450 nm) and may comprise a known stimulable phosphor sheet.Further, though not shown, a protective layer, a sensitizing layer andthe like may be provided.

The material for forming the photoconductive material layer 23 should bea material which exhibits conductivity upon exposure not only tostimulated emission L4 but also to the recording light L2 or momentarylight emitted from the stimulable phosphor layer 12 upon exposure to therecording light L2 when preliminary read-out is to be effectedsimultaneously with recording an image, though may be any material solong as it exhibits electric conductivity upon exposure to stimulatedemission emitted from the stimulable phosphor layer 12 when preliminaryread-out need not be effected simultaneously with recording an image. Inthe case of this embodiment where the stimulable phosphor layer 12 emitsblue stimulated emission in a wavelength range of not longer than 500 nm(e.g., near 400 nm), it is preferred that the material is a materialwhose major component is a-Se. The thickness of the photoconductivematerial layer 23 is preferably not smaller than 1 μm so that thephotoconductive material layer 23 absorbs a sufficient amount ofstimulated emission, an avalanche amplification effect can be obtainedand the level of signal to be taken out can be high enough. Further, itis preferred that the thickness of the photoconductive material layer 23be as large as possible in order to reduce the distribution capacity andsuppress fixed noise, but when the thickness is too large, the voltageof the power source for imparting the electric field becomes too high.Accordingly, in order to increase the ratio of the avalancheamplification effect to the fixed noise while taking into account thevoltage of the power source, the thickness of the photoconductivematerial layer 23 is preferably not smaller than 1 μm and not largerthan 100 μm, and more preferably not smaller than 10 μm and not largerthan 50 μm.

Further when the photoconductive material layer 23 is of a-Se, thephotoconductive material layer 23 is transparent to the red stimulatinglight and accordingly, the stimulating light L3 can be projected ontothe stimulable phosphor layer 12 through the photoconductive materiallayer 23.

The electrode elements 22 a of the first stripe electrode 22 extend insubstantially perpendicular to the electrode elements 26 a of the secondstrip electrode 26. The same number of electrode elements 22 a as thenumber of picture elements in the direction of the array of theelectrode elements 22 a are provided and the same number of electrodeelements 26 a as the number of picture elements in the direction of thearray of the electrode elements 26 a are provided. That is, the pitch ofthe electrode elements determines the pitch of the picture elements.When the electrode 22 of the first electrode layer 21 is thus divided bypicture element pitch so that each electrode element 22 a is inone-to-one correspondence with one picture element, the area of eachelectrode element 22 a is greatly reduced, whereby the dark current andthe output capacity are suppressed. Accordingly, dark current noiseand/or capacity noise are reduced and the S/N ratio of the image can beimproved.

When the stimulating light is to be projected onto the stimulablephosphor layer 12 from the side of the image read-out portion 20, it ispreferred that the first and second electrode layers 21 and 25 betransparent to the stimulating light. For this purpose, the electrodeelements 22 a and 26 a are suitably formed of known transparentconductive film such as ITO (Indium Tin Oxide) film. When electrodeelements 22 a and 26 a which are not transparent to the stimulatinglight are employed, at least the gaps 21 a and 25 a should betransparent to the stimulating light so that the stimulating light canimpinge upon the stimulable phosphor layer 12 through the gaps 21 a and25 a.

Further the second electrode layer 25 should be transparent to also thestimulated emission emitted from the stimulable phosphor layer 12. Forthis purpose, the electrode elements 26 a are suitably formed of knowntransparent conductive film such as ITO (Indium Tin Oxide) film.

FIGS. 2 and 3 show a radiation image recording and read-out system 110using the radiation image detecting sheet 1 of this embodiment. In FIG.2, the radiation image detecting sheet 1 is shown in a perspective view,and in FIG. 3 the radiation image detecting sheet 1 is shown in a X-Zcross-sectional view of the part indicated by arrow Q in FIG. 1.

The radiation image recording and read-out system 110 comprises theradiation image detecting sheet 1, a current detecting circuit 80, anA/D converter 86, a data correction section 87 and a ROM table 88. Thedata correction section 87 and the ROM table 88 are provided to suppressfluctuation of an image signal due to fluctuation of an electric fieldapplied to the photoconductive material layer 23. The radiation imagerecording and read-out system 110 is further provided with a radiationprojecting means 90 which emits radiation L1 such as X-rays so thatradiation L2 passing through an object 9 impinges upon the radiationimage detecting sheet 1 (the radiation L2 will be referred to as“recording light L2”, hereinbelow), and a stimulating light projectingmeans (stimulating light scanning means) 92 which projects stimulatinglight L3 onto the radiation image detecting sheet 1.

The radiation projecting means 90 and the stimulating light projectingmeans 92 are both disposed on the side of the first electrode layer 21of the image read-out portion 20 of the radiation image detecting sheet1, and the stimulating light projecting means 92, especially itsstimulating light source 92 a, is arranged to be retracted from theoptical path of the recording light L2, when radiation is projected fromthe radiation projecting means 90, not to interfere with the recordinglight L2.

The stimulating light projecting means 92 causes the stimulating lightL3, which is red light in a wavelength range not shorter than 600 nm andis in the form of a substantially uniform linear beam extendingsubstantially in perpendicular to the electrode elements 22 a of thefirst stripe electrode 22, to scan the radiation image detecting sheet 1in the longitudinal direction of the elements 22 a (sub-scanningdirection) from one edge to the other. As the stimulating light source92 a for emitting the stimulating light L3, an elongated, fluorescentlamp, LED, organic EL or the like can be used, and the stimulating lightprojecting means 92 causes the stimulating light L3 to scan theradiation image detecting sheet 1 by moving the stimulating light source92 a relatively to the radiation image detecting sheet 1. Further, thestimulating light source 92 a may comprise a plurality of linear sourcessuch as of liquid crystals or organic EL's which are arranged in a rowto form an area light source, and the stimulating light projecting means92 may be a means for energizing the linear sources in sequence. Such anarea light source formed of a number of linear sources may be formedintegrally with the radiation image detecting sheet 1.

Further, the stimulating light projecting means 92 may be arranged tocause a spot beam to scan the radiation image detecting sheet 1 in adirection substantially perpendicular to the elements 22 a (mainscanning direction) while moving the light source in the sub-scanningdirection relatively to the radiation image detecting sheet 1. Thestimulating light L3 may be either a continuous beam or a pulse beam.However, a high-power pulse beam is advantageous over a continuous beamin that a larger electric current can be detected and the S/N ratio ofthe image signal can be improved. Accordingly, in this particularembodiment, the stimulating light projecting means 92 projects ahigh-power pulse beam of about 100 μsec for each read-out line.

The current detecting circuit 80 is provided with a plurality of currentdetecting amplifiers 81 each comprising an operational amplifier 81 a,an integrating capacitor 81 b and a switch 81 c, and to the inversioninput terminal (−) of the operational amplifier 81 a is connected one ofthe elements 22 a of the first stripe electrode 22.

Further, the current detecting circuit 80 is provided with an electricvoltage imparting means 85 which comprises a power source 82, a switch83 and a switching portion 84 and imparts a predetermined electricvoltage between the electrode layers 21 and 25 of the image read-outportion 20, thereby applying an electric field to the photoconductivematerial layer 23. The switching portion 84 has a plurality of switchelements 84 a each comprising a fixed contact connected to one of theelements 26 a of the second strip electrode 26 and a movable contactconnected to the negative pole of the power source 82, whose positivepole is connected to non-inversion input terminals (+) of the respectiveoperational amplifiers 81 a by way of the switch 83.

The electric voltage imparting means 85 selectively closes the switchelements 84 a in response to movement of the stimulating light L3 underthe control of a control means (not shown) so that the electrode element26 a corresponding to the line just exposed to the stimulating light L3is electrically connected to the negative pole of the power source 82.With this arrangement, an electric voltage is imparted between theelectrode element 26 a corresponding to the line and all the electrodeelements 22 a from the power source 82 by way of the switch 83 and animaginary short circuit of the operational amplifier 81 a, whereby anelectric field is applied to the part of the photoconductive materiallayer 23 between the electrode elements 26 a and 22 a corresponding tothe line. The system may be arranged so that an electric voltage isimparted between several electrode elements 26 a including the electrodeelement 26 a corresponding to the line and all the electrode elements 22a.

The voltage of the power source 82 is set so that the potential gradientin the photoconductive material layer 23 becomes not lower than 10⁶V/cmand an avalanche amplification effect is generated in thephotoconductive material layer 23.

Each current detecting amplifier 81 detects an electric currentgenerated when electric charges generated upon exposure of thephotoconductive material layer 23 to stimulated emission L4 emitted fromthe stimulable phosphor layer 12 are read out from the image read-outportion 20 and reads out an image signal representing radiation energystored on the stimulable phosphor layer 12.

The A/D converter 86, the data correction section 87 and the ROM table88 (FIG. 3) connected downstream of the current detecting circuit 80 arefor correcting fluctuation in output data due to fluctuation in thevoltage of the power source 82. When the photoconductive material layer23 whose major component is a-Se is used under an electric field whichgenerates an avalanche amplification effect in the photoconductivematerial layer 23, the photoconductive material layer 23 becomessensitive to fluctuation of the electric voltage. Accordingly, it ispreferred that fluctuation of the voltage of the power source 82 besuppressed. It is further preferred that fluctuation in the output datawith fluctuation in the voltage of the power source 82 be stored and theoutput data be corrected according to fluctuation of the voltage of thepower source 82 during read-out of the image signal by, for instance,software processing. For this purpose, fluctuation in the output datawith fluctuation in the voltage of the power source 82 is stored in theROM table 88 and the data correction section 87 watches fluctuation inthe voltage of the power source 82 (more strictly the voltage across theelectrodes 22 and 26) during image read-out and corrects the output dataaccording to the fluctuation of the voltage of the power source.

The method of recording a radiation image of the object 9 on the imagerecording portion 10 and reading out the radiation image by the imageread-out portion 20 in the radiation image recording and read-out system110 will be described with reference to the timing chart shown in FIG.4, hereinbelow.

When a radiation image is to be recorded on the image recording portionof the radiation image detecting sheet 1, the switch 83 is turned off sothat an electric field is not applied to the photoconductive materiallayer 23 of the image read-out portion 20. Instead of turning off theswitch 83, all the switch elements 84 a of the switching portion 84 maybe opened.

Then radiation L1 is flashed onto the entire area of the object 9 at onetime so that recording light L2 bearing thereon a radiation image of theobject 9, which is the radiation L1 passing through the object 9, isprojected onto the first electrode layer 21 of the radiation imagedetecting sheet 1 for about one second. The recording light L2 passesthrough the image read-out section 20 of the radiation image detectingsheet 1 and impinges upon the stimulable phosphor layer 12. Thestimulable phosphor layer 12 stores radiation energy in proportion tothe intensity of the recording light L2, whereby a radiation image ofthe object 9 is stored on the image recording portion 10 of theradiation image detecting sheet 1.

Then the radiation L1 is stopped, and the switch 83 and all the switchelements 84 a of the switching portion 84 are once closed so that anelectric voltage is imparted between the first and second stripeelectrodes 22 and 26 by way of the switch 83 and an imaginary shortcircuit of the operational amplifier 81 a, and an electric field isapplied to the photoconductive material layer 23.

Then the stimulating light L3 is moved in the longitudinal direction ofthe electrode elements 22 a from one end thereof to the other end fromelectrode element 26 a to electrode element 26 a (sub-scanning) and isstopped at each electrode element 26 a for 100 μsec. During thesub-scanning, the switch elements 84 a are closed in sequence inresponse to the sub-scanning of the stimulating light L3 so that anelectric voltage is imparted between the electrode element 26 a of thesecond stripe electrode 22 corresponding to the read-out line (orseveral electrode elements 26 a including the electrode element 26 acorresponding to the read-out line) and all the electrode elements 22 aof the first stripe electrode 22 with the switch elements 84 a connectedto the other electrode elements 26 a kept open. With this arrangement,the distribution capacity established between the electrodes 22 a and 26a are reduced and fixed noise is minimized. Further, since one currentdetecting amplifier 81 is connected to each electrode element 22 a, andsimultaneous read-out can be effected in the main scanning direction inwhich the electrode elements 22 a are arranged, whereby the imageread-out time can be shortened.

Since being red light whose wavelength is not shorter than 600 nm, thestimulating light L3 is hardly absorbed by the photoconductive materiallayer 23 whose major component is a-Se and almost the whole stimulatinglight L3 impinges upon the stimulable phosphor layer 12. The part of thestimulable phosphor layer 12 exposed to the stimulating light L3 emitsblue stimulated emission L4 and the stimulated emission L4 impinges uponthe photoconductive material layer 23. In the photoconductive materiallayer 23, positive and negative charges are produced upon exposure tothe stimulated emission L4.

Further since a high electric field not lower than 10⁶V/cm has beenapplied between the electrode elements 22 a and 26 a corresponding tothe read-out line and an avalanche amplification effect is generated,whereby generation of positive and negative charges in thephotoconductive material layer 23 sharply increases. The quantumefficiency of the stimulable phosphor layer 12 is low and the stimulatedemission L4 from the stimulable phosphor layer 12 is weak. Accordingly,the amount of charges (the number of signal photons) generated byexposure to the stimulated emission is small. However, by virtue of theavalanche amplification effect, generation of the charges is multipliedand a sufficiently strong signal can be obtained, whereby the S/N ratiocan be increased.

Since an electric field has been applied to the photoconductive materiallayer 23, the negative charges transfer toward the electrode element 22a and the positive charges transfer toward the electrode element 26 a.

The operation amplifiers 81 a provided between the electrode elements 22a and 26 a simultaneously detect currents generated by said transfer ofthe charges element 22 a to element 22 a in response to the sub-scanningof the stimulating light L3 and switching of the switch elements 84 a ofthe switching portion 84, whereby an image signal is obtained. That is,an image signal representing the radiation image is obtained. Since thethickness of the photoconductive material layer 23 the major componentof which is a-Se is set not smaller than 1 μm and not larger than 100μm, the quantum efficiency to the blue stimulated emission, e.g., at 400nm, can be higher, e.g., 60 to 70%, than that in a photomultiplier or anavalanche photodiode using Si. Further since the read-out is effectedwith an electric field such as to generate an avalanche amplificationeffect applied to the photoconductive material layer 23 and correctionfor compensating for fluctuation of the voltage of the power source iseffected, the S/N ratio of the image can be greatly improved.

Further since fluctuation of the output data due to fluctuation of thevoltage of the power source 82 is corrected by the data correctionsection and the ROM table 88, the output data can be stably obtainedwithout being affected by fluctuation of the power source voltage,whereby the S/N ratio of the image signal can be further improved.

Further since the major component of the photoconductive material layer23 is a-Se, the ratio of the sensitivity to the stimulated emission(near 400 nm) to that to the stimulating light (600 to 700 nm) can besufficiently large. For example, in a state where no avalancheamplification effect is obtained, the ratio of the sensitivity to bluelight (470 nm) to that to red light (680 nm) is about 3.5 when thethickness of the a-Se layer is 10 μm. This value is very large ascompared with that (ratio of 2) when a photomultiplier is employed asthe photoelectric convertor means. As the thickness of the a-Se layer issmaller, the sensitivity to red light lowers and the blue/redsensitivity ratio increases and when an avalanche amplification effectis available, the blue/red sensitivity ratio further increases. Further,since Si is high in sensitivity to red light and low in sensitivity toblue light, Si is not suitable when the stimulated emission is blue.

Further since the photoconductive material layer 23 whose majorcomponent is a-Se and the stimulable phosphor layer 12 are integratedinto a radiation image detecting sheet 1, the radiation image detectingsheet 1 can be in the form of a solid to be strong against impact.Further since the photoconductive material layer 23 whose majorcomponent is a-Se can be formed by low-temperature deposition process, athin and large area radiation image detecting sheet 1 can be easilyproduced.

Further, since a stimulable phosphor layer 12 which does not store adark latent image upon exposure to radiation is employed in theradiation image detecting sheet 1 and since the photoconductive materiallayer 23 of the image read-out portion 20 does not form a chargecollecting portion where charges generated in the photoconductivematerial layer 23 collect, there does not arise a problem that a darklatent image is recorded due to a dark current even if an electric fieldis applied to the photoconductive material layer 23 during recording. Inother words, the photoconductive material layer 23 can be very high indark resistance (e.g., 10¹⁵ Ω·cm) as compared with a Si avalanchephotodiode. Even if a dark current should be generated, the dark currentis immediately discharged toward the current detecting amplifier 81 andthe current detecting amplifier 81 discharges the current, wherebyinfluence of a dark latent image can be avoided.

Further the photoconductive material layer 23 exhibits conductivity uponexposure not only to stimulated emission L4 but also to the recordinglight L2 or momentary light emitted from the stimulable phosphor layer12 upon exposure to the recording light L2. Accordingly, by projectingthe recording light L2 onto the radiation image detecting sheet 1 andintroducing the recording light L2 and/or the momentary light into thephotoconductive material layer 23 while applying an electric field tothe photoconductive material layer 23 and by detecting charges generatedin the photoconductive material layer 23, it is possible to obtain apreliminary read-out image signal bearing thereon a radiation imagewhile recording the radiation image on the stimulable phosphor layer 12.The radiation image recording and read-out system 110 can be used as itis as a system for obtaining such a preliminary read-out image signal,for instance, by using the current detecting circuit 80 as a means forreading out the preliminary read-out image signal. The preliminaryread-out image signal is used, for instance, for setting imageprocessing conditions in a final read-out. Further, the preliminaryread-out image signal can be used in place of a photo-timer to set theradiation projecting timing or to watch the amount of radiation.

When the radiation image recording and read-out system 110 is used as itis for preliminary read-out, one-dimensionally compressed informationintegrated in the longitudinal direction of the electrode element 22 ais obtained from each current detecting amplifier 81 as preliminaryread-out information, which cannot be constantly sufficient. In such acase, as shown in FIG. 5, by correcting the current detecting circuit 80so that each electrode element 22 a is directly connected to theinversion input terminal (−) and the non-inversion input terminal (+) isgrounded with the capacitor 81 b and the like left as they are, and byinserting between ground and each electrode element 26 a a signaldetecting amplifier 281 comprising an operational amplifier 281 acorresponding to the operational amplifier 81 a, a discrete power source282 a corresponding to the power source 82, a switch element 284 acorresponding to the switch element 84 a and a resister 285 connectedbetween the inversion input terminal (−) and the output terminal of theoperational amplifier 281 a, one-dimensionally compressed informationintegrated in the transverse direction of the electrode element 22 a isobtained from each additional signal detecting amplifier 281 in additionto one-dimensionally compressed information integrated in thelongitudinal direction of the electrode element 22 a obtained from eachcurrent detecting amplifier 81. On the basis of two pieces ofone-dimensionally compressed information, more detailed preliminaryread-out information can be obtained.

When the preliminary read-out image signal is unnecessary at the timethe final read-out is to be performed, the preliminary read-out imagesignal may be discharged. Further, the preliminary read-out image signalmay be added to a final read-out image signal obtained by the finalread-out.

Though, in the radiation image detecting sheet 1 of the firstembodiment, the image recording portion 10 and the image read-outportion 20 are superposed with the stimulable phosphor layer 12 and thesecond electrode layer 25 facing each other and the recording light L2and stimulating light L3 are projected from the side of the firstelectrode layer 21 of the image read-out portion 20, the recording lightL2 and stimulating light L3 may be projected from the side of the base11 of the image recording portion 10.

When the stimulating light L3 is projected from the side of the firstelectrode layer 21 of the image read-out portion 20, stimulated emissionL4 emitted from the front side of the stimulable phosphor layer 12 canbe detected and accordingly, an image of higher quality can be obtainedas compared with when the stimulating light L3 is projected from theside of the base 11 of the image recording portion 10.

On the other hand, when the recording light L2 and stimulating light L3are projected from the side of the base 11 of the image recordingportion 10, they can impinge upon the stimulable phosphor layer 12without passing through the stripe electrodes 22 and 26 of the imageread-out portion 20 and accordingly there does not arise a problem ofartifact due to the electrode matrix.

Further when the recording light L2 and stimulating light L3 areprojected from the side of the base 11 of the image recording portion10, a stimulating light cut filter can be inserted between thestimulable phosphor layer 12 and the second electrode layer 25 orbetween the second electrode layer 25 and the photoconductive materiallayer 23. Though it has been described that the red stimulating light L3is hardly absorbed by the photoconductive material layer 23, actuallythe photoconductive material layer 23 has slight sensitivity to thestimulating light L3 bearing thereon no image information, andaccordingly an offset current corresponding to weak charges generated bya slight amount of stimulating light L3 absorbed by the photoconductivematerial layer 23 is generated in the photoconductive material layer 23.When a stimulating light cut filter is inserted as described above,generation of such an offset current can be suppressed.

The image recording portion 10 and the image read-out portion 20 may besuperposed with the stimulable phosphor layer 12 and the first electrodelayer 21 facing each other.

FIG. 6 shows a radiation image detecting sheet 2 in accordance with asecond embodiment of the present invention. In the second and followingembodiments, the elements analogous to those shown in FIGS. 1A to 1C aregiven the same reference numerals and will not be described.

The radiation image detecting sheet 2 of this embodiment differs fromthe radiation image detecting sheet 1 of the first embodiment in thatanother (second) image read-out portion 30 is provided on the base 11 ofthe radiation image detecting sheet 1 of the first embodiment. That is,the second image read-out portion 30 comprises a first electrode layer31 (equivalent to the first electrode layer 21 of the first imageread-out portion 20), a photoconductive material layer 33 (equivalent tothe photoconductive material layer 23 of the first image read-outportion 20), and a second electrode layer 35, including electrodeportion 36 a, (equivalent to the second electrode layer 25 of the firstimage read-out portion 20) superposed one on another in this order, andis superposed on the base 11 with the second electrode layer 35 facingthe base 11. The base 11 is transparent to the stimulated emission L4.The second image read-out portion 30 may be superposed on the base 11with the first electrode layer 31 having electrode portions 31 a, 32 afacing the base 11.

As in the first embodiment, the material for forming the photoconductivematerial layer 23 should be a material which exhibits conductivity uponexposure not only to stimulated emission L4 but also to the recordinglight L2 or momentary light emitted from the stimulable phosphor layer12 upon exposure to the recording light L2 when preliminary read-out isto be effected simultaneously with recording an image.

The radiation image detecting sheet 2 of this embodiment is employed ina radiation image recording and read-out system which is equivalent tothe aforesaid system 110 plus a current detecting circuit, equivalent tothe current detecting circuit 80, for the second image read-out portion30. That is, in the radiation image recording and read-out system forthe radiation image detecting sheet 2 of this embodiment, the stimulatedemission L4 is detected by both the image read-out portions 10 and 30,whereby a pair of image signals on the basis of stimulated emission L4from one stimulable phosphor layer 12 are separately obtained. When thetwo image signals thus obtained are digitized and the two digital imagesignals thus obtained are added together to obtain an addition imagesignal, the S/N ratio can be improved. Also in this case, thephotoconductive material layer 23 is applied with an electric field suchas to generate an avalanche amplification effect in the photoconductivematerial lay 23. By virtue of the avalanche amplification effect, theamount of charges to be generated is increased, whereby a sufficientlylarge image signal can be obtained and the S/N ratio can be improved.The S/N ratio can be further improved by effecting the correction forcompensating for fluctuation of the voltage of the power source asdescribed above in conjunction with the first embodiment.

Further, by obtaining a pair of preliminary read-out image signals bythe pair of current detecting circuits 80 and adding together thepreliminary read-out image signals, a preliminary read-out image signalexcellent in S/N ratio can be obtained.

Further also in the radiation image detecting sheet 2 of thisembodiment, a stimulating light cut filter may be provided. For example,when the stimulating light L3 is to be projected from the second imageread-out portion side, the first image read-out portion 20 can beprovided with an offset current suppressing effect by inserting astimulating light cut filter between the stimulable phosphor layer 12and the second electrode layer 25 or between the second electrode layer25 and the photoconductive material layer 23. When the stimulating lightL3 is to be projected from the first image read-out portion side, thesecond image read-out portion 30 can be provided with an offset currentsuppressing effect by inserting a stimulating light cut filter betweenthe stimulable phosphor layer 12 and the base 11 or between the base 11and the second electrode layer 35 of the second image read-out portion30, or by coloring the base 11 in a color which absorbs the stimulatinglight L3.

FIG. 7 shows a radiation image detecting sheet 3 in accordance with athird embodiment of the present invention.

The radiation image detecting sheet 3 of this embodiment differs fromthe radiation image detecting sheet 1 of the first embodiment in thatanother (second) image recording portion 40 is provided on the firstelectrode layer 21 of the radiation image detecting sheet 1 of the firstembodiment. That is, the second image recording portion 40 comprises abase 41 (equivalent to the base 11 of the first image recording portion10), and a stimulable phosphor layer 42 (equivalent to the stimulablephosphor layer 12 of the first image recording portion 10), and issuperposed on the first electrode layer 21 with the stimulable phosphorlayer 42 facing the first electrode layer 11. The first electrode layer21 is transparent to the stimulated emission L4 emitted from thestimulable phosphor layer 42. The second image recording portion 40 maybe superposed on the first electrode layer 21 with the base 41 facingthe first electrode layer 21.

The radiation image detecting sheet 3 of this embodiment can be employedin the aforesaid system 110 as it is. Further, a stimulating light cutfilter may be inserted between the stimulable phosphor layer 12 and thesecond electrode layer 25 or between the second electrode layer 25 andthe photoconductive material layer 23 and another stimulating light cutfilter may be inserted between the stimulable phosphor layer 42 and thefirst electrode layer 21 or between the first electrode layer 21 and thephotoconductive material layer 23 so that stimulating light for thestimulable phosphor layer 12 and that for the stimulable phosphor layer42 are separately projected to the corresponding stimulable phosphorlayers from outside the image recording portions 10 and 40.

Since an image signal is obtained on the basis of the stimulatedemission from both the stimulable phosphor layers 12 and 42, the imagesignal can be high in the S/N ratio. Further a preliminary read-outimage signal which is high in the S/N ratio can be obtained.

FIGS. 8A to 8C show a radiation image detecting sheet 4 in accordancewith a fourth embodiment of the present invention.

The radiation image detecting sheet 4 of this embodiment differs fromthe radiation image detecting sheet 1 of the first embodiment in thatthe stripe electrode 26 of the second electrode layer 25 in theradiation image detecting sheet 1 of the first embodiment is changed toa flat electrode 26 c. Also the radiation image detecting sheet 4 can bemodified by adding one or more image recording portion or image read-outportion in the manner described above in conjunction with the second andthird embodiments.

The radiation image recording and read-out system using the radiationimage detecting sheet 4 of this embodiment may be substantially the sameas the radiation image recording and read-out system 110 shown in FIGS.2 and 3 except that the switching portion 84 of the current detectingcircuit 80 is removed and the flat electrode 26 c is directly connectedto the negative pole of the power source 82.

When the radiation image detecting sheet 4 of this embodiment isemployed, the image signal can be obtained without affected by switchingnoise which can be generated in the radiation image detecting sheet 1 ofthe first embodiment when the switch elements 84 a are switched. Furthersince the electrode 22 of the first electrode layer 21, which is themain electrode layer for detecting the charges, divided by pictureelement pitch so that each electrode element 22 a is in one-to-onecorrespondence with one picture element, the area of each electrodeelement 22 a is greatly reduced, whereby the dark current and the outputcapacity are suppressed. Accordingly, dark current noise and/or capacitynoise are reduced and the S/N ratio of the image can be improved.

FIGS. 9A to 9C show a radiation image detecting sheet 5 in accordancewith a fifth embodiment of the present invention.

The radiation image detecting sheet 5 of this embodiment differs fromthe radiation image detecting sheet 1 of the first embodiment in thatthe stripe electrode 22 of the first electrode layer 21 and the stripeelectrode 26 of the second electrode layer 25 in the radiation imagedetecting sheet 1 of the first embodiment are changed to flat electrodes22 c and 26 c. Also the radiation image detecting sheet 5 can bemodified by adding one or more image recording portion or image read-outportion in the manner described above in conjunction with the second andthird embodiments.

FIG. 10 shows a radiation image recording and read-out system 120 usingthe radiation image detecting sheet 5 of this embodiment.

The radiation image recording and read-out system 120 mainly differsfrom that 110 shown in FIGS. 2 and 3 in that the former 120 is providedwith a current detecting circuit 80 a including only one currentdetecting amplifier 81 whereas the current detecting circuit 80 of thelatter includes a plurality of current detecting amplifiers 81 one foreach electrode element 22 a. Further as in the fourth embodiment, theswitching portion 84 of the current detecting circuit 80 is removed andthe flat electrode 26 c is directly connected to the negative pole ofthe power source 82.

Further in the radiation image recording and read-out system 120, astimulating light projecting means 93 having a stimulating light source93 a which emits a red spot beam (not shorter than 600 nm) L3′ isemployed in place of the stimulating light projecting means 92 having astimulating light source 92 a which emits a linear beam. The stimulatinglight projecting means 93 causes the spot beam L3′ to two-dimensionallyscan the flat electrode 22 a over the entire area thereof. Thestimulating light projecting means 93 may comprise, for instance, aknown laser beam scanning optical system. Further, the stimulating lightsource 93 a may comprise a plurality of small point sources such as ofliquid crystals or organic EL's which are two-dimensionally arranged toform an area light source, and the stimulating light projecting means 93may be a means for energizing the point sources in sequence. Such anarea light source formed of a number of point sources may be formedintegrally with the radiation image detecting sheet 5. The stimulatinglight L3′ may be either a continuous beam or a pulse beam.

The method of reading out a radiation image stored on the imagerecording portion 10 of the radiation image detecting sheet 5 will bedescribed hereinbelow on only the difference from that when theradiation image detecting sheet 1 is employed. A radiation image isrecorded on the radiation image detecting sheet 5 in the same manner asthe radiation image detecting sheet 1.

When reading out a radiation image from the radiation image detectingsheet 5, the switch 83 is first turned so that an electric voltage isimparted between the flat electrodes 22 c and 26 c by way of animaginary short circuiting of the operational amplifier 81, therebyapplying an electric field to the photoconductive material layer 23.

Then, with the electric field kept applied to the photoconductivematerial layer 23, the stimulating light L3′ in the form of a spot beamis caused to scan the flat electrode 22 c over the entire area thereof.

Upon exposure to the stimulating light L3′, parts of the stimulablephosphor layer 12 emit stimulated emission L4 in proportion to thestored radiation energy and the stimulated emission L4 impinges upon thephotoconductive material layer 23 to produce positive and negativecharges in the photoconductive material layer 23.

Then by detecting an electric current flows through the imaginary shortcircuiting of the operational amplifier 81 a by the current detectingamplifier 81, an image signal representing the radiation image isobtained.

When the electric field applied to the photoconductive material layer 23is not lower than 10⁶V/cm, an avalanche amplification effect is obtainedand a sufficiently large image signal can be obtained.

Though radiation image detecting sheets in accordance with severalembodiments of the present invention and the radiation image recordingand read-out system in which the radiation image detecting sheets can besuitably used are described above, the radiation image detecting sheetsand the radiation image recording and read-out system can be variouslymodified, for instance, as follows.

stimulable phosphor layer stimulated emission: not longer than 500 nmnumber of layers 1, 2, . . . formed on 1st electrode layer, 2ndelectrode layer photoconductive material layer (a-Se) number of layers1, 2, . . . formed on surface of the stimulable phosphor layer, basefirst electrode layer stripe electrode, flat electrode second electrodelayer stripe electrode, flat electrode direction of incidence ofradiation from the image recording side, from the image read-out sidestimulating light (not shorter than 600 nm) line beam, spot beamdirection of incidence from the image recording side, from the imageread-out side continuous beam, pulse beam stimulating light cut filterprovided, not providedThe variations of the respective elements shown above may be combined inany manner. Further, the radiation and the stimulating light of theradiation image recording and read-out system may be variously modifiedaccording to the radiation image detecting sheet to be used. Forexample, when a radiation image detecting sheet in which a pair of imagerecording portions are provided with an energy absorbing memberinterposed therebetween and a pair of image read-out portions areprovided to separately receive the stimulated emission from the imagerecording portions is used, energy subtraction processing can be carriedout.

The elements may be variously modified other than the variations listedabove. For example, the base of the image recording portion may beremoved and the stimulable phosphor layer may be formed on the imageread-out portion. In any modification, a high electric field (e.g., notlower than 10⁶V/cm) is applied to the photoconductive material layer sothat an avalanche amplification effect is generated and the S/N ratio isimproved. Further, in any modification, the material for forming thephotoconductive material layer 23 should be a material which exhibitsconductivity upon exposure not only to stimulated emission L4 but alsoto the recording light L2 or momentary light emitted from the stimulablephosphor layer 12 upon exposure to the recording light L2 whenpreliminary read-out is to be effected simultaneously with recording animage.

Further, though, in the description above, the image recording portionand the image read-out portion or the stimulable phosphor layer and thesolid image sensor are integrated into a unit, they may be separate fromeach other. For example, a stimulable phosphor sheet and a solid imagesensor having the substantially same area may be opposed to each otherat a space from each other. As the stimulating light source, a linesource or a point source may be employed according to the form of theelectrode. Of course, image read-out is effected with an electric fieldsuch as to generate an avalanche amplification effect applied to thephotoconductive material layer.

The image recording portion or the solid image sensor can be employed asthe photoelectric convertor means in known systems for reading out aradiation image from a stimulable phosphor sheet where a photomultiplieris generally employed as the photoelectric convertor means.

FIGS. 11A and 11B show a radiation image read-out system 210 employing asolid image sensor in accordance with the present invention as aphotoelectric convertor means. The radiation image read-out system 210is substantially the same as that disclosed in our Japanese UnexaminedPatent Publication Nos. 55(1980)-12492 and 56(1981)-11395 except that asolid image sensor 223 of the present invention is employed in place ofa photomultiplier as the photoelectric convertor means. The stimulablephosphor layer of the stimulable phosphor sheet and the stimulatinglight may be the same as those in the first embodiment.

As shown in FIG. 11B, the solid image sensor 223 comprises a pair offlat electrodes 223 a and 223 b and a photoconductive material layer 223c sandwiched between the electrodes 223 a and 223 b and functions as azero-dimensional sensor. A light guide 222 is disposed to collectstimulated emission L4 emitted from a stimulable phosphor sheet 211 andthe stimulated emission L4 enters the light guide 222 through its lightinlet end face 222 a and is guided to its light outlet end faces 222 bin total reflection. The solid image sensor 223 is mounted on the lightoutlet end face 222 b of the light guide 222, and a stimulating lightcut filter 225 is disposed between the light outlet end face 222 b andthe electrode 223 a on the side of the light outlet end face 222 b.Since the photoconductive material layer 223 c is low in sensitivity tothe red stimulating light not shorter than 600 nm as described above,the stimulating light cut filter 225 may be thinner as compared withwhen a photomultiplier is employed. The flat electrode 223 a on the sideof the light outlet end face 222 b is made of a transparent conductivefilm such as an ITO film so that the stimulated emission L4 can impingeupon the photoconductive material layer 223 c. The other flat electrode223 b need not be transparent and may be of, for instance, aluminum. Themajor component of the photoconductive material layer 223 c is a-Se andthe stimulated emission L4 is blue light not longer than 500 nm. Thesize (detecting area) of the photoconductive material layer (a-Sephotoconductive film) 223 c should be sufficiently smaller than the sizeof the stimulable phosphor sheet 211. For example, when the size of thestimulable phosphor sheet 211 is 430 mm×430 mm, the size of thephotoconductive material layer 223 c should be not larger than 50 mm×50mm. When the area of the photoconductive material layer 223 c is small,generation of an excessive dark current can be avoided and load capacityis reduced, whereby the S/N ratio can be improved as compared with whenthe radiation image detecting sheet 1, where the stimulable phosphorlayer 12 and the photoconductive material layer 23 are of substantiallythe same area, is employed. The thickness of the photoconductivematerial layer 223 c is preferably not smaller than 1 μm and not largerthan 100 μm, and more preferably not smaller than 10 μm and not largerthan 50 μm so that the photoconductive material layer 223 c absorbs asufficient amount of stimulated emission L4, an avalanche amplificationeffect can be obtained and the fixed noise is suppressed. The voltage ofthe power source 82 is set so that the potential gradient in thephotoconductive material layer 223 c becomes not lower than 10⁶V/cm andan avalanche amplification effect is generated in the photoconductivematerial layer 223 c.

The stimulable phosphor sheet 211 is placed on a sheet conveyor means215 such as an endless belt and is conveyed in the direction of arrow Y(sub-scanning). A laser beam L3 (stimulating light) emitted from a laser216 is deflected by a rotary polygonal mirror 218 driven at a high speedby an electric motor 224 and travels through a condenser lens 219 suchas an fθ lens. Then the laser beam L3 is reflected by a mirror 220 toscan the stimulable phosphor sheet 211 in the direction of arrow X (mainscanning) which is substantially perpendicular to the sub-scanningdirection. Parts of the stimulable phosphor sheet 211 exposed to thelaser beam L3 emits stimulated emission L4 in proportion to storedradiation energy. The stimulated emission L4 enters the light guide 222through the light inlet end face 222 a and travels through the lightguide 222 repeating total reflection to impinge upon the solid imagesensor 223. Then charges according to the amount of the stimulatedemission L4 are generated in the photoconductive material layer 223 c ofthe solid image sensor 223 in the same manner as described above, andthe charges are detected by the current detecting circuit 80 a as animage signal.

Since the solid image sensor 223 can be smaller in both weight and sizeas compared with the photomultiplier, the overall radiation image readsystem 210 can be smaller in weight and size.

In the embodiment shown in FIGS. 12A and 12B, a long solid image sensor223 is employed. In FIGS. 12A and 12B, a stimulable phosphor sheet 211is placed on a pair of endless belts 215 a and 215 b which are driven byan electric motor (not shown). A laser 216 which emits a laser beam L3as the stimulating light, a rotary polygonal mirror 218 which is rotatedby an electric motor (not shown) to deflect the laser beam L3 and ascanning lens (fθ lens) 219 which converges the laser beam L3 deflectedby the polygonal mirror 218 onto the surface of the stimulable phosphorsheet 211 and causes the leaser beam L3 to scan the stimulable phosphorsheet 211 at a constant speed in the main scanning direction shown byarrow X are disposed above the stimulable phosphor sheet 211. The laserbeam L3 scans the stimulable phosphor sheet 211 in the main scanningdirection while the stimulable phosphor sheet 211 is conveyed in thesub-scanning direction shown by arrow Y by the endless belts 215 a and215 b, thereby two-dimensionally scanning the entire surface of thestimulable phosphor sheet 211.

A long solid image sensor 223 is disposed above the stimulable phosphorsheet 211 along the portion scanned by the laser beam L3 and receivesstimulated emission L4. Then an image signal representing the radiationimage stored on the stimulable phosphor sheet 211 is detected by thecurrent detecting circuit 80 a.

As shown in FIGS. 13A and 13B, the solid image sensor 223 comprises aglass substrate 226, a pair of long electrodes 223 a and 223 b and along photoconductive material layer 223 c sandwiched between theelectrodes 223 a and 223 b. The electrode pairs may comprise flatelectrodes. The photoconductive material layer 223 c exhibitsconductivity upon exposure to the stimulated emission L4 which impingesupon the photoconductive material layer 223 c through the glasssubstrate 226. The solid image sensor 223 functions as azero-dimensional sensor though large in length. The length of thephotoconductive material layer 223 c is substantially the same as thedimension of the stimulable phosphor sheet 211 in the main scanningdirection. The width of the photoconductive material layer (a-Sephotoconductive film) 223 c should be sufficiently smaller than the sizeof the stimulable phosphor sheet 211. For example, when the size of thestimulable phosphor sheet 211 is 430 mm×430 mm, the width of thephotoconductive material layer 223 c should be not larger than 50 mm.When the area of the photoconductive material layer 223 c is small,generation of an excessive dark current can be avoided and load capacityis reduced, whereby the S/N ratio can be improved as compared with whenthe radiation image detecting sheet 1, where the stimulable phosphorlayer 12 and the photoconductive material layer 23 are of substantiallythe same area, is employed. A stimulating light cut filter 225 isdisposed on the light inlet side of the glass substrate 226 (the side ofthe glass substrate 226 remote from the flat electrode 223 a) and theside surface of the glass substrate 226 and the stimulating light cutfilter 225 is covered with a light-shielding member 227. Since thephotoconductive material layer 223 c is low in sensitivity to the redstimulating light not shorter than 600 nm as described above, thestimulating light cut filter 225 may be thinner as compared with when aphotomultiplier is employed. The electrode 223 a through which thestimulated emission L4 enters the photoconductive material layer 223 cis made of a transparent conductive film such as an ITO film so that thestimulated emission L4 can impinge upon the photoconductive materiallayer 223 c. As in the embodiment shown in FIGS. 11A and 11B. thephotoconductive material layer 223 c includes a-Se as the majorcomponent and the thickness of the photoconductive material layer 223 cis preferably not smaller than 1 μm and not larger than 100 μm, and morepreferably not smaller than 10 μm and not larger than 50 μm. Thepotential gradient in the photoconductive material layer 223 c is setnot lower than 10⁶V/cm so that an avalanche amplification effect isgenerated in the photoconductive material layer 223 c. The solid imagesensor 223 may be formed to have a cylindrical light inlet end face asshown in FIG. 13B.

The long solid image sensor 223 can be smaller both in weight and sizeas compared with a long photomultiplier which has been conventionallyemployed, and accordingly the overall radiation image read system can besmaller in weight and size when the long solid image sensor 223 isemployed in place of the long photomultiplier. Further, the long solidimage sensor 223 such as 17 inches long can be easily produced at alower cost than a long photomultiplier or a long Si avalanchephotodiode.

The solid image sensor 223 shown in FIG. 13A or 13B can be variouslyemployed as the photoelectric convertor means in a radiation imageread-out system using a stimulable phosphor sheet as shown in FIGS. 14Ato 14C.

In the example shown in FIG. 14A, an elongated cylindrical mirror 235 isprovided to reflect stimulated emission L5, which travels away from thesolid image sensor 223, toward the solid image sensor 223. Thecylindrical 235 is held by a mirror mount 236 to extend in the directionof arrow X, i.e., in the main scanning direction and is opposed to thelight inlet end face 225 a of the stimulating light cut filter 225 ofthe solid image sensor 223 so that the stimulated emission L5 can beeffectively introduced into the solid image sensor 223.

In the example shown in FIG. 14B, a pair of solid image sensors 223 aredisposed on opposite sides of the portion of the stimulable phosphorsheet 211 along which the stimulating light L3 scans the stimulablephosphor sheet 211. A pair of image signals are detected by a pair ofcurrent detecting circuits 80 a respectively connected to the solidimage sensors 223, and the image signals are added by an adder 89 intoan addition image signal, whereby the detecting efficiency is increasedand the S/N ratio is improved.

In the example shown in FIG. 14C, an elongated cylindrical mirror 235 isprovided to reflect stimulated emission L5, which travels away from thesolid image sensor 223, toward the solid image sensor 223 as in theexample shown in FIG. 14A and at the same time, another solid imagesensor 223 is provided to detect stimulated emission L6 emitted downwardfrom the lower surface of the stimulable phosphor sheet 211. A pair ofimage signals are detected by a pair of current detecting circuits 80 arespectively connected to the solid image sensors 223, and the imagesignals are added by an adder 89 into an addition image signal, wherebythe S/N ratio is improved.

FIG. 15 shows a modification of the solid image sensor. The solid imagesensor 223 shown in FIG. 15 comprises a pair of solid image sensorelements 223 d, provided on a single elongated glass substrate 226spaced from each other in the transverse direction of the glasssubstrate 226. Each solid image sensor element 223 d comprises a pair ofelongated flat electrodes 223 a and 223 b and an elongatedphotoconductive material layer 223 c sandwiched between the electrodes223 a and 223 b, and is positioned on the glass substrate 226 with theflat electrode 223 b in contact with the glass substrate 226. Each solidimage sensor element 223 d is basically the same as the solid imagesensor 223 shown in FIG. 13A and a stimulating light cut filter 225 isprovided on the flat electrode 223 a through which the stimulatedemission L4 impinges upon the photoconductive material layer 223 c. Whena radiation image is to be read out by use of the solid image sensor 223shown in FIG. 15, the stimulating light L3 is caused to scan thestimulable phosphor sheet 211 through the glass substrate 226 betweenthe solid image sensor elements 223 d and then the stimulated emissionL4 emitted from the surface of the stimulable phosphor sheet 211 isdetected by both the solid image sensor elements 223 d. A pair of imagesignals are detected by a pair of current detecting circuits 80 arespectively connected to the solid image sensor elements 223 d as inthe example shown in FIG. 14B, and the image signals are added by anadder 89 into an addition image signal, whereby the S/N ratio isimproved. This modification is advantageous over the example shown inFIG. 14B in that the solid image sensor elements 223 d can be disposednearer to the stimulable phosphor sheet 211 than the pair of solid imagesensors 235 shown in FIG. 14B and accordingly the detecting efficiencyand/or the S/N ratio can be further improved.

The solid image sensor of the present invention may be a line sensor. Asolid image sensor in the form of a line sensor will be described withreference to FIGS. 16A and 16B, hereinbelow.

The solid image sensor 223 shown in FIGS. 16A and 16B is substantiallythe same as the solid image sensor shown in FIG. 12A except that theflat electrode 223 a is divided into a plurality elements arranged inthe longitudinal direction of the electrode 223 a. The other flatelectrode 223 b is left continuous. Specifically the elements of theflat electrode 223 a are arranged in pitches equal to the pictureelement pitches and each of the elements is not larger than the pictureelement pitches in the longitudinal direction of the electrode 223 a. Inthis specification, this will be expressed as “the electrode is dividedby picture element pitches”.

The solid image sensor 223 shown in FIGS. 17A and 17B is substantiallythe same as the solid image sensor shown in FIG. 15 except that each ofthe flat electrodes 223 a is divided into picture elements. The otherflat electrode 223 b is left continuous.

In the solid image sensors shown in FIGS. 16A and 16B and 17A and 17B,each of the electrode elements should be sufficiently small in width ascompared with the size of the stimulable phosphor sheet 211 (e.g., 430mm×430 mm) and should be, for instance, not larger than 50 mm. Thus,each of the solid image sensors can be used as a one-dimensional sensor(line sensor) in which a plurality of small solid image sensor elementsare arranged in a row. Each of the small solid image sensor elements areconnected to a current detecting amplifier similar to that shown in FIG.3.

When image read-out is effected by use of the line sensor shown in FIGS.16A and 16B or 17A and 17B, the line sensor is positioned in the samemanner as the solid image sensor 223 shown in FIG. 12A, and a linesource such as a fluorescent lamp, a cold cathode fluorescent lamp, anorganic EL array or a LED array which projects a line beam onto thestimulable phosphor sheet 211 while the stimulable phosphor sheet 211 ismoved in the sub-scanning direction may be used as the stimulating lightsource or a point light source which two-dimensionally scan thestimulable phosphor sheet 211 while the stimulable phosphor sheet 211 ismoved in the sub-scanning direction may be used as the stimulating lightsource. The electrode element 223 a of each solid image sensor elementis connected to a current detecting amplifier and image signals can besimultaneously read out in the main scanning direction in which thesolid image sensor elements are arranged, whereby the read-out time isshortened.

When a line light source 293 such as an organic EL array or a LED arrayis disposed on one side of the stimulable phosphor sheet 211 and thesolid image sensor in the form of a line sensor is disposed on the otherside of the stimulable phosphor sheet 211 as shown in FIG. 18A, theoverall system can be very small in height. The solid image sensor inthe form of a line sensor such as 17 inches long can be easily producedat a lower cost than a line sensor formed of Si avalanche photodiodes orthe like.

Other examples of using the solid image sensor in the form of a linesensor are shown in FIGS. 18B to 18D. The examples shown in FIGS. 18B to18D are basically the same as those shown in FIGS. 14A to 14C exceptthat the solid image sensor is a line sensor.

The solid image sensor in the form of a line sensor having a pair ofarrays of solid image sensor elements shown in FIGS. 17A and 17B may beemployed in the manner shown in FIG. 19A. Further, a solid image sensorin the form of a line sensor shown in FIGS. 16A and 16B may be added tothe arrangement shown in FIG. 19A as shown in FIG. 19B. With thearrangement shown in FIG. 19B, three image signals can be obtained andby adding the three image signals to a single addition image signal, theS/N ratio can be further improved. The long solid image sensor in theform of a zero-dimensional sensor shown in FIG. 15 may be employed inthe arrangement shown in FIG. 19B in place of the solid image sensor inthe form of a line sensor having a pair of arrays of solid image sensorelements shown in FIGS. 17A and 17B with the additional line sensorchanged to the zero-dimensional sensor shown in FIG. 13A.

A radiation image read-out system in accordance with a tenth embodimentof the present invention will be described, hereinbelow.

In FIGS. 20A and 20B, a stimulable phosphor sheet 211 is placed on apair of endless belts 215 a and 215 b which are driven by an electricmotor (not shown). A laser 216 which emits a laser beam L3 as thestimulating light, a rotary polygonal mirror 218 which is rotated by anelectric motor (not shown) to deflect the laser beam L3 and a scanninglens (fθ lens) 219 which converges the laser beam L3 deflected by thepolygonal mirror 218 onto the surface of the stimulable phosphor sheet211 and causes the leaser beam L3 to scan the stimulable phosphor sheet211 at a constant speed in the main scanning direction shown by arrow Xare disposed above the stimulable phosphor sheet 211. The laser beam L3scans the stimulable phosphor sheet 211 in the main scanning directionwhile the stimulable phosphor sheet 211 is conveyed in the sub-scanningdirection shown by arrow Y by the endless belts 215 a and 215 b, therebytwo-dimensionally scanning the entire surface of the stimulable phosphorsheet 211.

A long solid image sensor 223 is disposed above the stimulable phosphorsheet 211 along the portion scanned by the laser beam L3 and receivesstimulated emission L4. Upon exposure to the stimulated emission L4,electric charges are generated in the photoconductive material layer 223c of the solid image sensor 223 in proportion to the amount of thestimulated emission L4. The electric charges are detected by a currentdetecting circuit 80.

A stimulating light scanning means is formed by the laser 216, therotary polygonal mirror 218, the scanning lens 219, the drive means (notshown) and the like. As the stimulating light source, for instance, anLED array comprising a plurality of LEDs each stimulating a pictureelement on the stimulable phosphor sheet 211 may be used in place of thelaser 216.

As shown in FIGS. 21A to 21C, the solid image sensor 223 comprises aglass substrate 226, a pair of long flat electrodes 223 a and 223 b anda long photoconductive material layer 223 c sandwiched between the flatelectrodes 223 a and 223 b. The photoconductive material layer 223 cexhibits conductivity upon exposure to the stimulated emission L4 whichimpinges upon the photoconductive material layer 223 c through the glasssubstrate 226. The solid image sensor 223 functions as azero-dimensional sensor though large in length. A stimulating light cutfilter 225 is disposed on the light inlet side of the glass substrate226 (the side of the glass substrate 226 remote from the flat electrode223 a) and the side surface of the glass substrate 226 and thestimulating light cut filter 225 is covered with a light-shieldingmember 227. When red stimulating light bearing thereon no imageinformation impinges upon the photoconductive material layer 223 c,since the photoconductive material layer 223 c has slight sensitivity tothe stimulating light L3, an offset current corresponding to weakcharges generated by the stimulating light L3 is generated in thephotoconductive material layer 223. When a stimulating light cut filter225 is inserted as described above, only blue stimulated emission comesto impinge upon the photoconductive material layer 223 c with red light(not shorter than 600 nm) absorbed by the stimulating light cut filter225, and accordingly generation of such an offset current can besuppressed. Since the photoconductive material layer 223 c is low insensitivity to the red stimulating light not shorter than 600 nm asdescribed above, the stimulating light cut filter 225 may be thinner ascompared with when a photomultiplier is employed.

The flat electrode 223 a through which the stimulated emission L4 entersthe photoconductive material layer 223 c is made of a transparentconductive film such as an ITO film so that the stimulated emission L4can impinge upon the photoconductive material layer 223 c. The otherflat electrode 223 b need not be transparent and may be formed of, forinstance, aluminum.

The flat electrode 223 a which functions as a stimulated emissionreceiving face is divided into a plurality of electrode elements in thelongitudinal direction thereof (the main scanning direction) as shown inFIGS. 21B and 21C. With this arrangement, a plurality of photoelectricconversion segments which can function independently of each other areformed by the portions of the photoconductive material layer 223 cinterposed between the respective electrode elements of the flatelectrode 223 a and the flat electrode 223 b. The electrode 223 a may bedivided in various ways. For example, the electrode 223 a may be dividedzigzag as shown in FIG. 22B and may be divided in the sub-scanningdirection as shown in FIG. 22C. FIG. 22A shows the same division of theelectrode 223 a as that shown in FIGS. 21B and 21C.

The reason why the solid image sensor 223 is divided into a plurality ofphotoelectric conversion segments is to distribute the output capacityof the overall solid image sensor 223 to the photoelectric conversionsegments. By separately connecting current detecting amplifiers 81 tothe photoelectric conversion segments, generation of the dark current issuppressed and the output capacity of each photoelectric conversionsegment is reduced, whereby the S/N ratio is improved and an image of ahigher quality can be obtained.

For example, when a sensor having a photoconductive material of a-Se isexposed to a radiation of 80 Kev, 0.01 mR, several thousands to tenthousands of electrons are generated in the photoconductive materiallayer per picture element of 100 μm×100 μm. When the detecting amplifieris of a charge amplifier system, generated noise is represented by a+b×c(unit: e⁻, capacity noise is represented in terms of the number ofelectrons) wherein C (pF) represents the output capacity of thephotoelectric conversion segment (segment, 1, 2, . . . ) and a and b areconstants depending on the detecting amplifier. In a certain amplifier,a=550 and b=6.5, and the capacity noise was 550+6.5 C. In this case,when the output capacity of the photoelectric conversion segment is 100pF, the capacity noise is 1200 (e⁻). In accordance with ourinvestigation, when the capacity noise is at such a level, quality ofthe image is acceptable. That is, from the viewpoint of S/N ratio, it isconsidered that the capacity noise should be not higher than 1200 (e⁻),and accordingly, it is preferred that the output capacity of eachphotoelectric conversion segment be not larger than about 100 pF in thecase of the charge amplifier system.

In the case where the detecting amplifier 81 is of a current-voltageconversion system, it has found that quality of the image becomesacceptable when the output capacity is not larger than about 100 pF.That is, also in the case of the current-voltage conversion system, itis preferred that the output capacity of each photoelectric conversionsegment not larger than about 100 pF.

Accordingly, the electrode should be divided into a plurality ofelements so that the output capacity becomes not larger than 100 pFirrespective of the system of the detecting amplifier 81.

The detecting amplifier of a charge amplifier system utilizes thecharging voltage and the discharging voltage of a capacitor generated bycharge transfer and should be included in the current-voltage conversionsystem in view of the fact that an electric current generated by chargetransfer is converted to an electric voltage. However, in thisspecification, the current-voltage conversion system is to beinterpreted not to include the charge amplifier system. The detectingamplifiers of the current-voltage conversion system include alogarithmic amplifier.

The material for forming the photoconductive material layer 223 c shouldbe a material which exhibits conductivity upon exposure not only tostimulated emission L4 but also to the recording light L2 or momentarylight emitted from the stimulable phosphor layer 12 upon exposure to therecording light L2 when preliminary read-out is to be effectedsimultaneously with recording an image, though may be any material solong as it exhibits electric conductivity upon exposure to stimulatedemission L4 emitted from the stimulable phosphor layer 12 whenpreliminary read-out need not be effected simultaneously with recordingan image. In the case where the stimulable phosphor layer 212 emits bluestimulated emission in a wavelength range of not longer than 500 nm(e.g., near 400 nm), it is preferred that the material is a materialwhose major component is a-Se.

The thickness of the photoconductive material layer 223 c is preferablynot smaller than 1 μm so that the photoconductive material layer 223 cabsorbs a sufficient amount of stimulated emission L4, an avalancheamplification effect can be obtained and the level of signal to be takenout can be high enough. Further, it is preferred that the thickness ofthe photoconductive material layer 223 c be as large as possible inorder to reduce the distribution capacity and suppress fixed noise, butwhen the thickness is too large, the voltage of the power source forimparting the electric field becomes too high. Accordingly, in order toincrease the ratio of the avalanche amplification effect to the fixednoise while taking into account the voltage of the power source, thethickness of the photoconductive material layer 223 c is preferably notsmaller than 1 μm and not larger than 100 μm, and more preferably notsmaller than 10 m and not larger than 50 μm.

The length of the photoconductive material layer 223 c is setsubstantially the same as the dimension of the stimulable phosphor sheet211 in the main scanning direction. The width of the photoconductivematerial layer (a-Se photoconductive film) 223 c should be sufficientlysmaller than the size of the stimulable phosphor sheet 211. For example,when the size of the stimulable phosphor sheet 211 is 430 mm×430 mm, thewidth of the photoconductive material layer 223 c should be not largerthan 50 mm. When the area of the photoconductive material layer 223 c issmall, generation of an excessive dark current can be avoided and loadcapacity is reduced, whereby the S/N ratio can be improved as comparedwith when the stimulable phosphor layer 212 and the photoconductivematerial layer 223 c are of substantially the same area.

The long solid image sensor 223 can be smaller both in weight and sizeas compared with a long photomultiplier which has been conventionallyemployed, and accordingly the overall radiation image read system can besmaller in weight and size when the long solid image sensor 223 isemployed in place of the long photomultiplier. Further, the long solidimage sensor 223 such as 17 inches long can be easily produced at alower cost than a long photomultiplier or a long Si avalanchephotodiode.

FIG. 23 shows a circuit for reading out the electric charges from thesolid image sensor 223 and obtaining an image signal. As shown in FIG.23, the circuit comprises a current detecting circuit 80 connected tothe solid image sensor 223, an A/D converter 86, a data correctionsection 87 and a ROM table 88. The circuit further comprises a read-outcontrol circuit 300 connected between the current detecting circuit 80and the AID converter 86. The read-out control circuit 300 is forobtaining an image signal for one picture element by adding a pluralityof output signals from the detecting amplifiers 81 which receivestimulated emission from the picture element while switching the outputsignals in response to scanning of the stimulating light L3.

The current detecting circuit 80 is provided with a detecting amplifier81 of a charge amplifier system comprising an operational amplifier 81a, an integrating capacitor 81 b and switch 81 c. The current detectingamplifier 81 detects an electric current generated when electric chargesgenerated upon exposure of the photoconductive material layer 223 c tostimulated emission L4 emitted from the stimulable phosphor layer 212are read out and reads out an image signal representing radiation energystored on the stimulable phosphor layer 212 disposed on a substrate 213.

As shown in FIG. 23, the current detecting circuit 80 is provided with aplurality of current detecting amplifiers 81, and to the inversion inputterminals (−) of the operational amplifiers 81 a are discretelyconnected the electrode elements of the stripe electrode 223. That is,the flat electrode 223 a which functions as a stimulated emissionreceiving face is divided in the longitudinal direction (the mainscanning direction) into a plurality of electrode elements to formphotoelectric conversion segments which function independently of eachother. The photoelectric conversion segments are discretely connected tothe detecting amplifiers 81. With this arrangement, input capacity ofeach detecting amplifier 81 is reduced and the stability of the circuitcan be ensured.

Further, the current detecting circuit 80 is provided with an electricvoltage imparting means 85 which comprises a power source 82 and aswitch 83 and imparts a predetermined electric voltage between theelectrodes 223 a and 223 b of the solid image sensor 223, therebyapplying an electric field to the photoconductive material layer 223 c.The positive pole of the power source 82 is connected to non-inversioninput terminals (+) of the respective operational amplifiers 81 a by wayof the switch 83. The voltage of the power source 82 is set so that thepotential gradient in the photoconductive material layer 223 c becomesnot lower than 10⁶V/cm and an avalanche amplification effect isgenerated in the photoconductive material layer 223 c.

The A/D converter 86, the data correction section 87 and the ROM table88 connected downstream of the current detecting circuit 80 are forcorrecting fluctuation in output data due to fluctuation in the voltageof the power source 82. When the photoconductive material layer 223 cwhose major component is a-Se is used under an electric field whichgenerates an avalanche amplification effect in the photoconductivematerial layer 223 c, the photoconductive material layer 223 c becomessensitive to fluctuation of the electric voltage. Accordingly, it ispreferred that fluctuation of the voltage of the power source 82 besuppressed. It is further preferred that fluctuation in the output datawith fluctuation in the voltage of the power source 82 be stored and theoutput data be corrected according to fluctuation of the voltage of thepower source 82 during read-out of the image signal by, for instance,software processing. For this purpose, fluctuation in the output datawith fluctuation in the voltage of the power source 82 is stored in theROM table 88 and the data correction section 87 watches fluctuation inthe voltage of the power source 82 (more strictly the voltage across theelectrodes 223 a and 223 b) during image read-out and corrects theoutput data according to the fluctuation of the voltage of the powersource.

When the image signal is to be read out from the stimulable phosphorsheet 211, the switch 83 is closed so that an electric voltage isimparted between the electrodes 223 a and 223 b by way of the switch 83and an imaginary short circuit of the operational amplifier 81 a, and anelectric field is applied to the photoconductive material layer 223 c.

Then the stimulating light L3 in the form of a line beam is caused toscan the entire area of the stimulable phosphor sheet 211 with theelectric field kept applied to the photoconductive material layer 223 c.That is, while the stimulable phosphor sheet 211 storing thereon aradiation image is conveyed in the direction of arrow Y (sub-scanning)by the endless belts 215 a and 215 b, the stimulating light L3 emittedfrom the laser 216 is deflected by the rotary polygonal mirror 218 toimpinge upon the stimulable phosphor sheet 211 through the scanning lens219 and scan the stimulable phosphor sheet 211 in the main scanningdirection shown by the arrow X substantially perpendicular to thesub-scanning direction. The parts of the stimulable phosphor sheet 211exposed to the stimulating light L3 emit stimulated emission L4, whichis blue light near 400 nm, and the stimulated emission L4 impinges uponthe solid image sensor 223.

In the photoconductive material layer 223 c of the solid image sensor223, positive and negative charges are generated upon exposure to thestimulated emission L4 in proportion to the amount of the stimulatedemission L4. Since an electric field is applied to the photoconductivematerial layer 223 c, the negative charges transfer toward the electrode223 a and the positive charges transfer toward the electrode 223 b.

Further since a high electric field not lower than 10⁶V/cm has beenapplied between the electrode elements 223 a and 223 b corresponding tothe read-out line and an avalanche amplification effect is generated,whereby generation of positive and negative charges in thephotoconductive material layer 223 c sharply increases. The quantumefficiency of the stimulable phosphor layer 212 is low and thestimulated emission L4 from the stimulable phosphor layer 212 is weak.Accordingly, the amount of charges (the number of signal photons)generated by exposure to the stimulated emission is small. However, byvirtue of the avalanche amplification effect, generation of the chargesis multiplied and a sufficiently strong signal can be obtained, wherebythe S/N ratio can be increased.

The operation amplifiers 81 a provided between the electrodes 223 a and223 b detect currents generated by said transfer of the charges, wherebyan image signal is obtained. That is, an image signal representing theradiation image is obtained. Since the thickness of the photoconductivematerial layer 223 c the major component of which is a-Se is set notsmaller than 1 μm and not larger than 100 μm, the quantum efficiency tothe blue stimulated emission, e.g., at 400 nm, can be higher, e.g., 60to 70%, than that in a photomultiplier or an avalanche photodiode usingSi. Further since the read-out is effected with an electric field suchas to generate an avalanche amplification effect applied to thephotoconductive material layer 223 c and correction for compensating forfluctuation of the voltage of the power source is effected, the S/Nratio of the image can be greatly improved.

Further since fluctuation of the output data due to fluctuation of thevoltage of the power source 82 is corrected by the data correctionsection and the ROM table 88, the output data can be stably obtainedwithout being affected by fluctuation of the power source voltage,whereby the S/N ratio of the image signal can be further improved.

Further since the major component of the photoconductive material layer223 c is a-Se, the ratio of the sensitivity to the stimulated emission(near 400 nm) to that to the stimulating light (600 to 700 nm) can besufficiently large. For example, in a state where no avalancheamplification effect is obtained, the ratio of the sensitivity to bluelight (470 nm) to that to red light (680 nm) is about 35 when thethickness of the a-Se layer is 10 μm. This value is very large ascompared with that (ratio of 2 when a photomultiplier is employed as thephotoelectric convertor means. As the thickness of the a-Se layer issmaller, the sensitivity to red light lowers and the blue/redsensitivity ratio increases and when an avalanche amplification effectis available, the blue/red sensitivity ratio further increases.

The effect of dividing the flat electrode 223 a which forms thestimulated emission receiving face will be described with reference toFIGS. 24A and 24B, hereinbelow.

The case where the electrode 223 a is divided in the manner shown inFIG. 22A will be described first. As shown in FIG. 24A, the read-outcontrol circuit 300 comprises a switching means 301 which switches inresponse to the main scanning position of the stimulating light L3 thesignals from the detecting amplifiers 81 connected to the respectivephotoelectric conversion segments 1 to 4, an adder means 302 which addsthe signals passing through the switching means 301, and a bufferamplifier 303. The output signal of the buffer amplifier 303 is inputinto the A/D converter 86. The switching means 301 comprises a pluralityof movable switches connected between the respective detectingamplifiers 81 and the adder means 302.

A control signal CTL which is generated on the basis of a startingsignal representing a start point of the main scanning is input into theswitching means 301 from a circuit for controlling the scanning positionof the stimulating light L3 (not shown). As shown in FIG. 24B, theswitching means 301 switches the signals from the detecting amplifiers81 in response to the main scanning position of the stimulating lightL3. That is, as the stimulating light L3 scans the stimulable phosphorsheet 211 in the main scanning direction, the parts exposed to thestimulating light L3 (picture element positions) emit stimulatedemission L4 in sequence. As shown in FIG. 23, the stimulated emission L4travels obliquely upward as well as just upward. Accordingly, near theboundaries of the photoelectric conversion segments, the stimulatedemission L4 from one picture element position impinges upon a pluralityof photoelectric conversion segments, and accordingly, if the signalsare switched so that an image signal is obtained on the basis of theoutput signal from only one photoelectric conversion segment, theobtained image signal cannot be constantly sufficient. Accordingly, animage signal for a picture element the stimulated emission from which isreceived by a plurality of photoelectric conversion segments is obtainedby adding the output signals from the detecting amplifiers 81 connectedto the photoelectric conversion segments which receive the stimulatedemission from the picture element. For example, at the boundary betweenthe segment 1 and the segment 2, the switching means 301 closes theswitches connected to the segment 1 and the segment 2 so that the outputsignals from the corresponding detecting amplifiers 81 are added by theadder means 302. (1+2) At the boundary between the segment 2 and thesegment 3, the switching means 301 closes the switches connected to thesegment 2 and the segment 3 so that the output signals from thecorresponding detecting amplifiers 81 are added by the adder means 302.(2+3) At the boundary between the segment 3 and the segment 4, theswitching means 301 closes the switches connected to the segment 3 andthe segment 4 so that the output signals from the correspondingdetecting amplifiers 81 are added by the adder means 302. (3+4) At theparts other than the boundaries, the switching means 301 closes only oneof the switches so that the output signal of only one of the amplifiers81 is input into the adder means 302.

The case where the electrode 223 a is divided in the manner shown inFIG. 22B will be described next. In this case, since the electrode 223 ais divided zigzag at angles to the main scanning direction, thestimulated emission L4 impinges upon a plurality of segments at theboundaries therebetween even if the stimulated emission L4 travels onlyjust upward. Accordingly, as in the case shown in FIG. 24B, an imagesignal for a picture element the stimulated emission from which isreceived by a plurality of photoelectric conversion segments is obtainedby adding the output signals from the detecting amplifiers 81 connectedto the photoelectric conversion segments which receive the stimulatedemission from the picture element. For example, at the boundary betweenthe segment 1 and the segment 2, the switching means 301 closes theswitches connected to the segment 1 and the segment 2 so that the outputsignals from the corresponding detecting amplifiers 81 are added by theadder means 302. (1+2)

Though, in this case, the period for which the image signals are addedbecomes longer since the boundaries between the segments are zigzag, thejoints of the image signals become more smooth and unevenness of animage can be avoided since the stimulated emission gradually shifts fromone segment to another. Taking into account the part of the stimulatedemission L4 which travels obliquely upward, the period for which theimage signals are added may be further extended in the manner similar tothat shown in FIG. 24B.

When the electrode 223 a is divided in the sub-scanning direction asshown in FIG. 22C, the switching need not be effected.

A radiation image read-out system in accordance with an eleventhembodiment of the present invention will be described with reference toFIGS. 26A to 26C and 27, hereinbelow.

FIGS. 26A to 26C show the solid image sensor employed in thisembodiment. As shown in FIGS. 26A to 26C, the electrodes 223 a and 223 bare divided in the main scanning direction in the same manner into aplurality of elements so that each element of one of the electrode isopposed to one of the elements of the other electrode with thephotoconductive material layer 223 c intervening therebetween. With thisarrangement, a plurality of photoelectric conversion segments whichfunction independently of each other are formed.

The purpose of dividing not only the electrode 223 a but also theelectrode 223 b is for not only distributing the output capacity of theoverall solid image sensor 223 to the segments in order to reduce thedark current and/or the output capacity but also facilitatingcontrolling on and off (active and inactive) of the segments.

FIG. 27 shows a circuit for obtaining an image signal from the solidimage sensor shown in FIGS. 26A to 26C with the electrodes 223 a and 223b are divided in the manner shown in FIG. 22A.

In this embodiment, the read-out control means 300 comprises an addermeans 302 which is connected to the elements of the electrode 223 a ofthe segment 1 to segment 4 and adds the signals from the respectiveelements of the electrode 223 a, a buffer amplifier 303, a switchingmeans 304 which is connected to the elements of the electrode 223 b ofthe segment 1 to segment 4 and switches on and off of the segments inresponse to the scanning position of the stimulating light L3, and aplurality of discrete power sources 382 a which discretely supply apredetermined voltage to the elements of the electrode 223 b through theswitching means 304. The output signal of the buffer amplifier 303 isinput into the A/D converter 86. The switching means 304 is providedwith a plurality of switches connected between the elements of theelectrode 223 b and the discrete power sources 382 a. A control signalCTL is input into the switching means 304 from a circuit for controllingthe scanning position of the stimulating light L3 (not shown). Theoperation of the switching means 304 is substantially the same as thatshown in FIG. 24B except that the segments are turned on and offindependently of each other and the output signals of the segments areadded. That is, in this embodiment, the switching means 304 controls onand off the segments by controlling on and off of the electric voltagesapplied to the respective segments from the discrete power sources 382 aor on and off of the electric fields applied to the photoconductivematerial layer 223 c between the elements of the electrodes 223 a and223 b. With this arrangement, only photoelectric conversion segmentswhich are effective in reading out the image signal, that is, only thesegments which are actually exposed to the stimulated emission L4, canbe made active while the other photoelectric conversion segments keptinactive. Accordingly influence of the dark current in the solid imagesensor 223 and/or false signals due to residual charges can besuppressed, influence of flare can be avoided and the S/N ratio can begreatly improved. This effect cannot be obtained by simply dividing thephotoelectric convertor means, for instance, in the tenth embodiment.

An image signal for a picture element the stimulated emission from whichis received by a plurality of photoelectric conversion segments isobtained by adding the output signals from the segments which receivethe stimulated emission from the picture element by the adder means 302in the basically the same manner as described above in conjunction withFIG. 24B.

Further since the segments which simultaneously receive stimulatedemission from one picture element shift with the scanning position ofthe stimulating light L3. Accordingly, the image signals from thesegments to be added are switched in response to the scanning of thestimulating light L3. This switching is carried out by turning on andoff the segments by the switching means 304. When the electrodes aredivided in the manner shown in FIG. 22B, the switching is carried out inthe same manner as that described above in conjunction with FIG. 25B.

Though, in the tenth and eleventh embodiments, the electrode of a longzero-dimensional solid image sensor is divided in the main scanningdirection or in the sub-scanning direction, the electrode of azero-dimensional solid image sensor which is square and is smaller thanthe stimulable phosphor sheet in area may be divided in the mainscanning direction or in the sub-scanning direction. Also in this case,it is preferred that the outputs of actually effective photoelectricconversion segments be added and the actually effective photoelectricconversion segments be switched in response to the scanning position ofthe stimulating light.

1. An image read-out method of obtaining an image signal bearing thereonimage information by use of a stimulable phosphor sheet having a layerof stimulable phosphor which emits stimulated emission in proportion tothe stored energy of radiation upon exposure to stimulating light and asolid image sensor having a photoconductive material layer whichexhibits electric conductivity upon exposure to the stimulated emissionfrom the stimulable phosphor sheet, and by scanning with stimulatinglight a stimulable phosphor sheet which has been exposed to radiationand has stored thereon an image, causing the photoconductive materiallayer to be exposed to stimulated emission emitted from the stimulablephosphor sheet upon exposure to the stimulating light, and detectingelectric charges generated in the photoconductive material layer uponexposure to the stimulated emission, comprising: using the solid imagesensor having a photoconductive material layer having an area smallerthan the area of the stimulable phosphor sheet and the stimulatedemission receiving face of the solid image sensor is divided into aplurality of photoelectric conversion segments, and discretelyconnecting a plurality of image signal obtaining means to the respectivephotoelectric conversion segments to detect electric charges generatedin the photoelectric conversion segments, and obtaining an image signalfor one picture element by adding a plurality of image signals obtainedfrom a plurality of image signal obtaining means, said plurality ofimage signal obtaining means being respectively connected to a pluralityof photoelectric conversion segments which receive stimulated emissionfrom the picture element, and said plurality if image signal obtainingmeans being connected to an adder, wherein the plurality of imagesignals comprise signals obtained from adjacent photoelectric conversionelements having activation times that overlap for at least a period oftime.
 2. An image read-out method as defined in claim 1 in which theimage signals from the image signal obtaining means which are to beadded are switched in response to scanning of the stimulating light. 3.An image read-out method as defined in claim 1 in which the stimulablephosphor sheet having a layer of stimulable phosphor which is stimulatedby stimulating light in a wavelength range of not shorter than 600 nmand emits stimulated emission in a wavelength range of not longer than500 nm is used, and the solid image sensor having a photoconductivematerial layer whose major component is a-Se is used.
 4. An imageread-out method as defined in claim 1 wherein the output capacitance ofeach of said photoelectric conversion segments is not larger than 100pF.
 5. An image read-out method of obtaining an image signal bearingthereon image information by use of a stimulable phosphor sheet having alayer of stimulable phosphor which emits stimulated emission inproportion to the stored energy of radiation upon exposure tostimulating light and a solid image sensor having a photoconductivematerial layer which exhibits electric conductivity upon exposure to thestimulated emission from the stimulable phosphor sheet, and by scanningwith stimulating light a stimulable phosphor sheet which has beenexposed to radiation and has stored thereon an image, causing thephotoconductive material layer to be exposed to stimulated emissionemitted from the stimulable phosphor sheet upon exposure to thestimulating light, and detecting electric charges generated in thephotoconductive material layer upon exposure to the stimulated emissionby applying an electric field to the photoconductive material layer,comprising: using a solid image sensor whose photoconductive materiallayer has an area smaller than the area of the stimulable phosphor sheetand whose stimulated emission receiving face is divided into a pluralityof photoelectric conversion segments, and activating the photoelectricconversion segments to be active or inactive independently of eachother, such that a timing of activation of adjacent photoconversionelements overlaps for at least a period of time.
 6. An image read-outmethod as defined in claim 5 in which the photoelectric conversionsegments are made active or inactive by controlling application of theelectric field to the photoconductive material layer.
 7. An imageread-out method as defined in claim 5 in which making active or inactivethe photoelectric conversion segment is controlled in response toscanning of the stimulating light.
 8. An image read-out method asdefined in claim 5 in which an image signal for one picture element isobtained by adding a plurality of output signals from a plurality ofphotoelectric conversion segments which receive stimulated emission fromthe picture element.
 9. An image read-out method as defined in claim 8in which the output signals from the photoelectric conversion segmentswhich are to be added are switched in response to scanning of thestimulating light.
 10. The method of claim 8, wherein at least two ofthe plurality of photoelectric conversion segments are located adjacentto each other and provide image signals during activation times thatoverlap for at least a period of time.
 11. An image read-out method asdefined in claim 5 in which the stimulable phosphor sheet having a layerof stimulable phosphor which is stimulated by stimulating light in awavelength range of not shorter than 600 nm and emits stimulatedemission in a wavelength range of not longer than 500 nm is used, andthe solid image sensor having a photoconductive material layer whosemajor component is a-Se is used.
 12. An image read-out method as definedin claim 5 wherein the output capacitance of each of said photoelectricconversion segments is not larger than 100 pF.
 13. An image read-outsystem comprising a stimulating light source which emits stimulatinglight, a stimulating light scanning means which causes the stimulatinglight emitted from the stimulating light source to scan a stimulablephosphor sheet having a layer of stimulable phosphor which emitsstimulated emission in proportion to the stored energy of radiation uponexposure to the stimulating light, a solid image sensor having aphotoconductive material layer which exhibits electric conductivity uponexposure to the stimulated emission from the stimulable phosphor sheet,and an image signal obtaining means which detects electric chargesgenerated in the photoconductive material layer of the solid imagesensor when the stimulable phosphor sheet is exposed to the stimulatinglight and stimulated emission emitted from the stimulable phosphor sheetimpinges upon the photoconductive material, and obtains an image signalrepresenting an image stored on the stimulable phosphor sheet, whereinthe solid image sensor has a photoconductive material layer having anarea smaller than the area of the stimulable phosphor sheet and thestimulated emission receiving face of the solid image sensor is dividedinto a plurality of photoelectric conversion segments, and a pluralityof image signal obtaining means are discretely connected to therespective photoelectric conversion segments, and further comprising anadder connected to said plurality of image signal obtaining means, saidadder obtaining an image signal for one picture element by adding aplurality of image signals obtained from a plurality of image signalobtaining means, which are respectively connected to a plurality ofphotoelectric conversion segments which receive stimulated emission fromthe picture element, wherein the adder adds the plurality of imagesignals, said plurality of image signals comprise signals obtained fromadjacent photoelectric conversion elements having activation times thatoverlap for at least a period of time.
 14. An image read-out system asdefined in claim 13 further comprising a switching means which switchesthe image signals from the image obtaining means which are to be addedin response to scanning of the stimulated light.
 15. An image read-outsystem as defined in claim 13 in which the stimulable phosphor sheet hasa layer of stimulable phosphor which is stimulated by stimulating lightin a wavelength range of not shorter than 600 nm and emits stimulatedemission in a wavelength range of not longer than 500 nm, and the solidimage sensor has a photoconductive material layer whose major componentis a-Se.
 16. An image read-out system comprising a stimulating lightsource which emits stimulating light, a stimulating light scanning meanswhich causes the stimulating light emitted from the stimulating lightsource to scan a stimulable phosphor sheet having a layer of stimulablephosphor which emits stimulated emission in proportion to the storedenergy of radiation upon exposure to the stimulating light, a solidimage sensor having a photoconductive material layer which exhibitselectric conductivity upon exposure to the stimulated emission from thestimulable phosphor sheet, an electric voltage imparting means whichimparts an electric voltage to the photoconductive material layer of thesolid image sensor to apply an electric field to the photoconductivematerial layer and an image signal obtaining means which detectselectric charges generated in the photoconductive material layer of thesolid image sensor when the stimulable phosphor sheet is exposed to thestimulating light and stimulated emission emitted from the stimulablephosphor sheet impinges upon the photoconductive material with theelectric field applied to the photoconductive material layer, andobtains an image signal representing an image stored on the stimulablephosphor sheet wherein the solid image sensor has a photoconductivematerial layer having an area smaller than the area of the stimulablephosphor sheet and the stimulated emission receiving face of the solidimage sensor is divided into a plurality of photoelectric conversionsegments, and there is provided a control means which makes active orinactive the photoelectric conversion segments independently of eachother, such that a timing of activation of adjacent photoconversionelements overlaps for at least a period of time.
 17. An image read-outsystem as defined in claim 16 in which the control means makes active orinactive the photoelectric conversion segments by controllingapplication of the electric field to the photoconductive material layer.18. An image read-out system as defined in claim 16 in which the controlmeans makes active or inactive the photoelectric conversion segments inresponse to scanning of the stimulating light.
 19. An image read-outsystem as defined in claim 16 further comprising an adder means whichobtains an image signal for one picture element by adding a plurality ofoutput signals from a plurality of photoelectric conversion segmentswhich receive stimulated emission from the picture element.
 20. An imageread-out system as defined in claim 19 further comprising a switchingmeans which switches the output signals from the photoelectricconversion segments which are to be added in response to scanning of thestimulating light.
 21. The system of claim 19, wherein at least two ofthe plurality of photoelectric conversion segments are located adjacentto each other and provide image signals during activation times thatoverlap for at least a period of time.
 22. An image read-out system asdefined in claim 16 in which the stimulable phosphor sheet has a layerof stimulable phosphor which is stimulated by stimulating light in awavelength range of not shorter than 600 nm and emits stimulatedemission in a wavelength range of not longer than 500 nm, and the solidimage sensor has a photoconductive material layer whose major componentis a-Se.